code: public static boolean isUSPhoneNumber(String s) {
          if (isEmpty(s)) return defaultEmptyOK;
          String normalizedPhone = stripCharsInBag(s, phoneNumberDelimiters);
  
          return (isInteger(normalizedPhone) && normalizedPhone.length() == digitsInUSPhoneNumber);
      }
docs: isUSPhoneNumber returns true if string s is a valid U.S. Phone Number.  Must be 10 digits.