str_replace should work just fine. Check out the code below
$phone = "555-174-3268";
$phone = str_replace("-", "", $phone);
$phone = str_replace(".", "", $phone);
$phone = str_replace(" ", "", $phone);
$phone = str_replace("(", "", $phone);
$phone = str_replace(")", "", $phone);
On the last two with the parenthesis, you may need to escape the parenthesis to avoid parse errors.
Cgraz