Apple has just updated their Apple TV Remote App and it works great. Assuming you have the new Apple TV and are familiar with the new remote control then the interface will feel very familiar.
The new Apple TV Remote App is great for searching and entering usernames and passwords by typing. Sure you could just use the Siri Microphone button and talk to either the remote or remote app. So many choices. The iPhone is already full of sensors, so it can also be used as a game controller for Apple TV games.
If nothing else, this app will buy you some time if you manage to loose your real remote.