Wordpress function advice - is this possible to target a specific function and execute another function after it?

Question

Ok... so working on a theme designed by Astoundify... which although beautiful has been disgustingly made.

Also using WP Job Manager.

Have created a new custom field, 'fax'. Want fax to display after the phone number. Astoundify has nicely made this display on the theme using a widget - making the WP Job Manager hooks completely useless.

What i need to do is get that fax number to display immediately after phone. Is this possible to do with the functions file so that i don't have to modify the core files?

The following is the code which is outputting the phone number:

public static function the_phone() {
    global $post;

    $phone = $post->_phone;

    if ( ! $phone ) {
        return;
    }


?>
    <div class="job_listing-phone">
        <span itemprop="telephone"><a href="tel:<?php echo esc_attr( preg_replace( "/[^0-9,.]/", '', $phone ) ); ?>"><?php echo
        esc_attr( $phone ); ?></a></span>
    </div>
<?php
}

And i am trying to output the fax using the following:

add_action( 'single_job_listing_start', 'display_fax_number_data', 50 );

function display_fax_number_data() {
  global $post;

  $fax = get_post_meta( $post->ID, '_fax', true );

  if ( $fax ) {
    echo '<li>' . __( 'Fax:' ) . ' ' . $fax . '</li>';
  }
}

And its working... just not in the right place. Have lost a day trying to do something that should have been so simple.

Any help appreciated.