Gravity Forms New Zealand phone number validation mask

functions.php

add_filter( 'gform_phone_formats', 'nz_phone_format' );
// NZ phone format - 8, 9 or 10 digits long
function anz_phone_format( $phone_formats ) {
    $phone_formats['nz'] = array(
        'label'       => 'New Zealand',
        'mask'        => '99 9999 99?99',
        'regex'       => '/^(?:(?:\+?64[2-9]|0[2-9])\d{6,7}|(?:\+?642\d{1}|02\d{1})\d{6,8}|(?:(?:\+?64800|0800)|(?:\+?64508|0508))\d{6,8})$/',
        'instruction' => 'New Zealand phone numbers.',
    );
    return $phone_formats;
}