execute(modelValue, regionCode) {
    if (!PhoneUtilManager.isLoaded) {
      // Return a Promise once not loaded yet. Since async Validators are meant for things like
      // loading server side data (in this case a lib), we continue as a sync Validator once loaded
      return new Promise(resolve => {
        PhoneUtilManager.loadComplete.then(() => {
          resolve(hasFeedback(modelValue, regionCode));
        });
      });
    }
    return hasFeedback(modelValue, regionCode);
  }
@param {string} modelValue telephone number without country prefix
@param {RegionCode} regionCode