leaky-paywall-simplecirc-phone.php

<?php 

add_filter('leaky_paywall_simplecirc_subscriber_data', 'zeen_tester_add_phone');

function zeen_tester_add_phone( $data )
{
  
  // this is the name of the field generated by the Leaky Paywall Custom Registration Fields add-on.  
  // Please change the field name to whatever is being used in your own custom field for phone number.
  if ( !isset($_POST['0_field_1_1'] ) ) {
    return $data;
  }

    $data['phone'] = sanitize_text_field( $_POST['0_field_1_1']);
    
    return $data;

}