Format phone number in US format

function.php

function format_phone_us($phone) {
	// note: making sure we have something
	if(!isset($phone{3})) { return ''; }
	// note: strip out everything but numbers
	$phone = preg_replace("/[^0-9]/", "", $phone);
	$length = strlen($phone);
	switch($length) {
		case 7:
			return preg_replace("/([0-9]{3})([0-9]{4})/", "$1-$2", $phone);
			break;
		case 10:
			return preg_replace("/([0-9]{3})([0-9]{3})([0-9]{4})/", "($1) $2-$3", $phone);
			break;
		case 11:
			return preg_replace("/([0-9]{1})([0-9]{3})([0-9]{3})([0-9]{4})/", "$1($2) $3-$4", $phone);
			break;
		default:
			return $phone;
			break;
	}
}

// usage
$phone = '2142234736';
$phone = format_phone_us( $phone);
echo $phone;