function getPhoneConfirmationCodeErrorMessage() {
  var element = goog.dom.getElementByClass(
      'firebaseui-id-phone-confirmation-code-error', container);
  assertFalse(goog.dom.classlist.contains(element, 'firebaseui-hidden'));
  return goog.dom.getTextContent(element);
}
@return {?string} The phone code verification error message.