$re = '/\d(?:_*\d){9}|\+?\d_*\d[\s\-]?(?:_*\d){8,11}|\d[ -]?\d{3}[ -]?\d{3}[ -]?\d{4}/u';
$str = '+2348066421534';
preg_match_all($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