$re = '/(?<!\d)\d{3}[.\s-]?\d{3}[.\s-]?\d{4}(?!\d)/';
$str = '18005555555
80055555551
"8005555555"
8005555555
800.555.5555
"s8005555555"';
preg_match_all($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