/**
* WordPress Plugin: Masks Form Fields - https://wordpress.org/plugins/masks-form-fields/
* PHP - Custom script to add mask in input phone the WooCommerce. /wp-content/themes/YOUR-THEME/functions.php
*/
add_action('wp_footer', function () {echo "<script type=\"text/javascript\">jQuery(document).ready(function($){ $(\"input[name='billing_phone']\").addClass(\"phone_us\"); });</script>";}, 11);