$re = '/^(?=(-?\d){10,14}$)3[0-9-]{9,18}$/m';
$str = '312345678
312345678912345
3-12345678
3-12345678912345
3-1-2-3-4-5-67891234
12345678901
3-1-23456789
3-1-2-34567891234
3123456789
31234567891234
';
preg_match_all($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