$re = '/^(\()?(?P<area>\d{3})(?(1)\))[ -]?(?P<fst>\d{3})-?(?P<lst>\d{4})$/m';
$str = '(321) 123-4567
(321) 1234567
321-123-4567
321123-4567';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php