```dart
Future<void> signUpWithPhoneVerification(
  String username,
  String password,
) async {
  await Amplify.Auth.signUp(
    username: username,
    password: password,
    options: CognitoSignUpOptions(
      userAttributes: <CognitoUserAttributeKey, String>{
        // ... if required
        CognitoUserAttributeKey.email: 'test@example.com',
        CognitoUserAttributeKey.phoneNumber: '+18885551234',
      },
    ),
  );
}
```