$re = '/(?=^\d+)^([78]\d{10}|[1]\d{9}|[0](?:\d{6}[78]|\d{7}[1])(?:\d{10}|\d{9}))/m';
$str = '85556987456
75556987456
1555698745
000000085556987456
000000075556987456
000000001556987456';
preg_match_all($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