Remove the Phone field from the required billing fields for PMPro checkout.

pmpro-dont-require-billing-fields.php

<?php
/**
 * This recipe can be used to remove the Phone and Address 2 fields
 * from the required billing fields for checkout.
 *
 * Note: Make sure your Gateway doesn't require it also.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function pmpro_dont_require_billing_fields( $fields ) {
	unset( $fields['bphone'] );
	return $fields;
}
add_filter( 'pmpro_required_billing_fields', 'pmpro_dont_require_billing_fields' );