<?php

add_action('init', 'jmd_phone_field_format');

function jmd_phone_field_format(){

	 $args = array(
        'post_type' => 'job_listing',
        'post_status' => 'publish',
        'posts_per_page'   => -1
    );
    $posts = get_posts($args);
    foreach ( $posts as $post ) {

	$string = get_post_meta($post->ID, '_job_phone', true);
	preg_match_all('/^\D?(\d{3})\D?\D?(\d{3})\D?(\d{4})$/i', $string, $matches);
		if ( ! empty ($matches[1]) ) {
		$output = '(' . $matches[1][0] . ')' ." ". $matches[2][0] .'-' . $matches[3][0];
		update_post_meta( $post->ID, '_job_phone', $output );
		}
	}
}