Clean 10 Digit Phone Number

private function _remove_non_numeric($string) {
		return preg_replace('/\D/', '', $string);
	}
 
	private function _clean_phone_number($phone_number)
	{
		$CI = &get_instance();
 
		$phone_number = $CI->_remove_non_numeric($phone_number);
 
			if((strlen($phone_number) >= 11) AND ($phone_number[0] == '1'))
			{
				$string = substr($phone_number, 1);
			}
 
		return $phone_number;
	}