hooking-into-wordpress-business-directory.php

<?php
add_filter('wpbdp_form_field_html_value', 'alter_wpbdp_form_field_html_value', 10, 3);
function alter_wpbdp_form_field_html_value($value, $post_id, $class)
{
    // add tel: to phone numbers
    if($class->get_id() == 6) // the ID of the field to modify
    {
        $value = '<a href="tel:'.preg_replace('/[^0-9]/', '', $value).'">'.$value.'</a>';
    }
 
    return $value;
}