Make billing details optional for Paid Memberships Pro

billing-fields-optional.php

<?php
//add lines 4-15 to your custom plugin or functions.php of your active theme

function pmpro_remove_bfields( $pmpro_required_billing_fields ){

    //remove field ID's from array to make fields required
    $remove_field = array('bphone');

    //loop through the $remove_field array and unset each billing field to make it optional.
    foreach($remove_field as $field){
        unset($pmpro_required_billing_fields[$field]);
    }            

    return $pmpro_required_billing_fields;
}

add_filter('pmpro_required_billing_fields', 'pmpro_remove_bfields');