$re = '/(\((21|11)\) 9|\((?!21|11)\d{2}\) )[6789]\d{3}-\d{4}/';
$str = '(21) 96000-0000
(21) 6000-0000
(10) 6000-0000
(10) 96000-0000';
preg_match_all($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