핸드폰 구분자 넣기

function format_phone($phone){
    $phone = preg_replace("/[^0-9]/", "", $phone);
    $length = strlen($phone);
   
    switch($length){
        case 11 :
            return preg_replace("/([0-9]{3})([0-9]{4})([0-9]{4})/", "$1-$2-$3", $phone);
            break;
        case 10:
            return preg_replace("/([0-9]{3})([0-9]{3})([0-9]{4})/", "$1-$2-$3", $phone);
            break;
        case 9:
            return preg_replace("/([0-9]{2})([0-9]{3})([0-9]{4})/", "$1-$2-$3", $phone);
            break;
        default :
            return $phone;
            break;
    }
}