$re = '/1[5-9]\d{2,}|[2-9]\d{3,}|1\d{4,}/';
$str = '800
0800
1234
1511
1555
1789
2111
2345
3456
56756
123123
123123123
159999999999';
preg_match_all($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