How add custom field to notification e-mail ?

Hello,

I have form with custom field for Phone. I need that after successful registration will come email with all form field to my email.

I was use @hartsig2000 hack:

You can edit Pages.php (in /mailpoet/lib/Subscription) and add after

$this->subscriber->save();

the following code:

$to = ‘YOUR_MAILADRESS’;
$subject = ‘The subject’;
$body = $this->subscriber->first_name . ‘ ‘ . $this->subscriber->last_name . ‘ (‘ . $this->data[’email’] . ‘) just subscribed.’;
$headers = array(‘Content-Type: text/html; charset=UTF-8’);
wp_mail( $to, $subject, $body, $headers );

and this working for me, but how can I add custom field “Phone” to this mail… ?
https://i.imgur.com/Nd3Zf6K.png
https://i.imgur.com/jgD4r7G.png

The page I need help with: [log in to see the link]