symfony Form with multiple steps - forms

Question

I am trying to create a form with multiple steps in that:
First field displayed should be a phone number type.
Once that is submitted I want to perform a lookup to see if there is a user with that phone number.
If a user is found then I need a second field for verification, so I create a zip code field.
I am currently doing this with one controller and one form type:
SearchType:
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder->add('phoneNumber', PhoneNumberType::class, array(
'default_region' => 'US',
'format' => PhoneNumberFormat::NATIONAL))
->add("finished", HiddenType::class, array(
"data" => "no"))
->add("submit", SubmitType::class);
$formModifier = function (FormInterface $form) {
$phoneNumber = $form->get('phoneNumber')->getData();
$one = $this->em->getRepository('AppBundle:Phone')->findOneByPhoneNumber($phoneNumber);
if($one){
$form->remove("submit");
$form->remove("finished");
$form->add("zipCode", TextType::class);
$form->add("finished", HiddenType::class, array(
"data" => "yes"));
$form->add("submit", SubmitType::class);
}
};
$builder->addEventListener(
FormEvents::PRE_SET_DATA,
function (FormEvent $event) use ($formModifier) {
$formModifier($event->getForm());
}
);
$builder->get('phoneNumber')->addEventListener(
FormEvents::POST_SUBMIT,
function (FormEvent $event) use ($formModifier) {
$formModifier($event->getForm()->getParent());
}
);
}
Controller:
$form = $this->createForm(SearchType::class);
$form->handleRequest($request);
if ($form->isSubmitted() && $form->isValid() && $form->get("finished")->getData() == "Yes") {
//...
}
So, I'm not even sure if I am on the right track. I am currently trying to use the Hidden field "finished" to let me controller know when to actually do the work with the submitted data, however "finished" never gets set to "yes" and I am not sure why.
Aside from that, is there a better way for me to be doing this?
I looked into CraueFormFlowBundle but that required the underlying data to be an object (wouldn't work with Array) and I didn't think I wanted it to be in this case since I am just using the data entered to perform a query.