Add custom validator on phone number of customer addres book form (theme) - magento2

Question

I am completely new at magento 2. I want to add custom validation on phone number in customer address book form which can be seen after login by customer. Below is UI.
Form UI:
customer address book form after login
This UI form code is located under app/design/frontend/vendor/template/address/edit.phtml
Code looks like below:
<?php
/**
* Copyright © Magento, Inc. All rights reserved.
* See COPYING.txt for license details.
*/
/** #var \Magento\Customer\Block\Address\Edit $block */
?>
<?php $_company = $block->getLayout()->createBlock(\Magento\Customer\Block\Widget\Company::class) ?>
<?php $_telephone = $block->getLayout()->createBlock(\Magento\Customer\Block\Widget\Telephone::class) ?>
<?php $_fax = $block->getLayout()->createBlock(\Magento\Customer\Block\Widget\Fax::class) ?>
<form class="form-address-edit"
action="<?= $block->escapeUrl($block->getSaveUrl()) ?>"
method="post"
id="form-validate"
enctype="multipart/form-data"
data-hasrequired="<?= $block->escapeHtmlAttr(__('* Required Fields')) ?>"
data-mage-init='{"validation":{
"rules": {
"telephone": {
"required":false,
"digits": digits
}
}
}}'>
<fieldset class="fieldset">
<legend class="legend"><span><?= $block->escapeHtml(__('Contact Information')) ?></span></legend><br>
<?= $block->getBlockHtml('formkey') ?>
<input type="hidden" name="success_url" value="<?= $block->escapeUrl($block->getSuccessUrl()) ?>">
<input type="hidden" name="error_url" value="<?= $block->escapeUrl($block->getErrorUrl()) ?>">
<?= $block->getNameBlockHtml() ?>
<?php if ($_company->isEnabled()) : ?>
<?= $_company->setCompany($block->getAddress()->getCompany())->toHtml() ?>
<?php endif ?>
<?php if ($_telephone->isEnabled()) : ?>
<?= $_telephone->setTelephone($block->getAddress()->getTelephone())->toHtml() ?>
<?php endif ?>
<?php if ($_fax->isEnabled()) : ?>
<?= $_fax->setFax($block->getAddress()->getFax())->toHtml() ?>
<?php endif ?>
</fieldset>
<fieldset class="fieldset">
<legend class="legend"><span><?= $block->escapeHtml(__('Address')) ?></span></legend><br>
<?php $_streetValidationClass = $this->helper(\Magento\Customer\Helper\Address::class)->getAttributeValidationClass('street'); ?>
<div class="field street required">
<label for="street_1" class="label">
<span><?= /* #noEscape */ $block->getAttributeData()->getFrontendLabel('street') ?></span>
</label>
<div class="control">
<input type="text"
name="street[]"
value="<?= $block->escapeHtmlAttr($block->getStreetLine(1)) ?>"
title="<?= /* #noEscape */ $block->getAttributeData()->getFrontendLabel('street') ?>"
id="street_1"
class="input-text <?= $block->escapeHtmlAttr($_streetValidationClass) ?>"/>
<div class="nested">
<?php $_streetValidationClass = trim(str_replace('required-entry', '', $_streetValidationClass)); ?>
<?php for ($_i = 1, $_n = $this->helper(\Magento\Customer\Helper\Address::class)->getStreetLines(); $_i < $_n; $_i++) : ?>
<div class="field additional">
<label class="label" for="street_<?= /* #noEscape */ $_i + 1 ?>">
<span><?= $block->escapeHtml(__('Street Address %1', $_i + 1)) ?></span>
</label>
<div class="control">
<input type="text" name="street[]"
value="<?= $block->escapeHtmlAttr($block->getStreetLine($_i + 1)) ?>"
title="<?= $block->escapeHtmlAttr(__('Street Address %1', $_i + 1)) ?>"
id="street_<?= /* #noEscape */ $_i + 1 ?>"
class="input-text <?= $block->escapeHtmlAttr($_streetValidationClass) ?>">
</div>
</div>
<?php endfor; ?>
</div>
</div>
</div>
<?php if ($this->helper(\Magento\Customer\Helper\Address::class)->isVatAttributeVisible()) : ?>
<div class="field taxvat">
<label class="label" for="vat_id">
<span><?= /* #noEscape */ $block->getAttributeData()->getFrontendLabel('vat_id') ?></span>
</label>
<div class="control">
<input type="text"
name="vat_id"
value="<?= $block->escapeHtmlAttr($block->getAddress()->getVatId()) ?>"
title="<?= /* #noEscape */ $block->getAttributeData()->getFrontendLabel('vat_id') ?>"
class="input-text <?= $block->escapeHtmlAttr($this->helper(\Magento\Customer\Helper\Address::class)->getAttributeValidationClass('vat_id')) ?>"
id="vat_id">
</div>
</div>
<?php endif; ?>
<div class="field city required">
<label class="label" for="city"><span><?= /* #noEscape */ $block->getAttributeData()->getFrontendLabel('city') ?></span></label>
<div class="control">
<select name="city" id="city" class="<?= $block->escapeHtmlAttr($this->helper(\Magento\Customer\Helper\Address::class)->getAttributeValidationClass('city')) ?>" title="<?= $block->escapeHtmlAttr(__('City')) ?>" data-validate="{'validate-select':true}">
<?php
$cityArr = $block->getCityFromAPI();
if( is_array($cityArr) && !empty($cityArr) ){
foreach( $cityArr as $city ){
$selected = ( $block->escapeHtmlAttr($block->getAddress()->getCity()) == $city['value'] ) ? 'selected="selected"' : '' ;
echo '<option value="'.$city['value'].'" '.$selected.'>'.$city['label'].'</option>';
}
}
?>
</select>
</div>
</div>
<div class="field region required">
<label class="label" for="region_id">
<span><?= /* #noEscape */ $block->getAttributeData()->getFrontendLabel('region') ?></span>
</label>
<div class="control">
<select id="region_id" name="region_id"
title="<?= /* #noEscape */ $block->getAttributeData()->getFrontendLabel('region') ?>"
class="validate-select region_id" <?= /* #noEscape */ !$block->getConfig('general/region/display_all') ? ' disabled="disabled"' : '' ?>>
<option value=""><?= $block->escapeHtml(__('Please select a region, state or province.')) ?></option>
</select>
<input type="text"
id="region"
name="region"
value="<?= $block->escapeHtmlAttr($block->getRegion()) ?>"
title="<?= /* #noEscape */ $block->getAttributeData()->getFrontendLabel('region') ?>"
class="input-text validate-not-number-first <?= $block->escapeHtmlAttr($this->helper(\Magento\Customer\Helper\Address::class)->getAttributeValidationClass('region')) ?>"<?= !$block->getConfig('general/region/display_all') ? ' disabled="disabled"' : '' ?>/>
</div>
</div>
<div class="field zip required">
<label class="label" for="zip">
<span><?= /* #noEscape */ $block->getAttributeData()->getFrontendLabel('postcode') ?></span>
</label>
<div class="control">
<input type="text"
name="postcode"
value="<?= $block->escapeHtmlAttr($block->getAddress()->getPostcode()) ?>"
title="<?= /* #noEscape */ $block->getAttributeData()->getFrontendLabel('postcode') ?>"
id="zip"
class="input-text validate-zip-international <?= $block->escapeHtmlAttr($this->helper(\Magento\Customer\Helper\Address::class)->getAttributeValidationClass('postcode')) ?>">
<div role="alert" class="message warning" style="display:none">
<span></span>
</div>
</div>
</div>
<div class="field country required">
<label class="label" for="country"><span><?= /* #noEscape */ $block->getAttributeData()->getFrontendLabel('country_id') ?></span></label>
<div class="control">
<?= $block->getCountryHtmlSelect() ?>
</div>
</div>
<?php if ($block->isDefaultBilling()) : ?>
<div class="message info">
<span><?= $block->escapeHtml(__("It's a default billing address.")) ?></span>
</div>
<?php elseif ($block->canSetAsDefaultBilling()) : ?>
<div class="field choice set billing">
<input type="checkbox" id="primary_billing" name="default_billing" value="1" class="checkbox">
<label class="label" for="primary_billing">
<span><?= $block->escapeHtml(__('Use as my default billing address')) ?></span>
</label>
</div>
<?php else : ?>
<input type="hidden" name="default_billing" value="1" />
<?php endif; ?>
<?php if ($block->isDefaultShipping()) : ?>
<div class="message info">
<span><?= $block->escapeHtml(__("It's a default shipping address.")) ?></span>
</div>
<?php elseif ($block->canSetAsDefaultShipping()) : ?>
<div class="field choice set shipping">
<input type="checkbox" id="primary_shipping" name="default_shipping" value="1" class="checkbox">
<label class="label" for="primary_shipping">
<span><?= $block->escapeHtml(__('Use as my default shipping address')) ?></span>
</label>
</div>
<?php else : ?>
<input type="hidden" name="default_shipping" value="1">
<?php endif; ?>
</fieldset>
<div class="actions-toolbar">
<div class="primary">
<button type="submit"
class="action save primary"
data-action="save-address"
title="<?= $block->escapeHtmlAttr(__('Save Address')) ?>">
<span><?= $block->escapeHtml(__('Save Address')) ?></span>
</button>
</div>
<div class="secondary">
<a class="action back btn btn-light" href="<?= $block->escapeUrl($block->getBackUrl()) ?>">
<span><?= $block->escapeHtml(__('Go back')) ?></span>
</a>
</div>
</div>
</form>
<script type="text/x-magento-init">
{
"#form-validate": {
"addressValidation": {
"postCodes": <?= /* #noEscape */ $block->getPostCodeConfig()->getSerializedPostCodes(); ?>
}
},
"#country": {
"regionUpdater": {
"optionalRegionAllowed": <?= /* #noEscape */ $block->getConfig('general/region/display_all') ? 'true' : 'false' ?>,
"regionListId": "#region_id",
"regionInputId": "#region",
"postcodeId": "#zip",
"form": "#form-validate",
"regionJson": <?= /* #noEscape */ $this->helper(\Magento\Directory\Helper\Data::class)->getRegionJson() ?>,
"defaultRegion": "<?= (int) $block->getRegionId() ?>",
"countriesWithOptionalZip": <?= /* #noEscape */ $this->helper(\Magento\Directory\Helper\Data::class)->getCountriesWithOptionalZip(true) ?>
}
}
}
</script>
So How can I add validation on phone number field in below code?
<?php if ($_telephone->isEnabled()) : ?>
<?= $_telephone->setTelephone($block->getAddress()->getTelephone())->toHtml() ?>
<?php endif ?>