A couple of years ago our Global-Game-Jam game ‘InVected’ (ElixirForum topic) used Phoenix in a similar way, where Phoenix manages a web-interface that people connect to on their mobile phone, which turns their phone in a joystick.
Phoenix then forwards the state-changes to the main game (written with Unity and its C#-dialect) running on a large screen.
The phones are connected to Phoenix over a websocket. Phoenix is connected to the Unity game using a TCP socket.
This is of course Jam-code and as such quite messy, but maybe it helps.
GitHub repository of the game
