code: function onLinkReauthVerifyPhoneNumber() {
    var phoneNumber = $('#link-reauth-phone-number').val();
    var provider = new firebase.auth.PhoneAuthProvider(auth);
    // Clear existing reCAPTCHA as an existing reCAPTCHA could be targeted for a
    // sign-in operation.
    clearApplicationVerifier();
    // Initialize a reCAPTCHA application verifier.
    makeApplicationVerifier('link-reauth-verify-phone-number');
    provider.verifyPhoneNumber(phoneNumber, applicationVerifier)
        .then(function(verificationId) {
          clearApplicationVerifier();
          $('#link-reauth-phone-verification-id').val(verificationId);
          alertSuccess('Phone verification sent!');
        }, function(error) {
          clearApplicationVerifier();
          onAuthError(error);
        });
  }
docs: Sends a phone number verification code for linking or reauth.