(Pocket-lint) - You can now use your mobile phone as a touch controller for Stadia on a TV.
Alternatively, you can hook up a third-party controller to your Android phone or iPhone, either via USB or Bluetooth, and use the mobile device as a wireless bridge to control Stadia games.
Admittedly, that way adds a little extra latency, but it's a great workaround for using a USB controller or wireless pad not supported by Chromecast Ultra, say. The latter TV device only accepts the official Stadia controller.
According to Google Stadia support (via Android Authority), it's easy to link your phone with Stadia running on an Android TV or Google TV device. You just launch the Stadia app on your television, launch the app on Android or iOS, then tap controller (just make sure all apps are updated to the latest versions).
It's a little harder for Chromecast Ultra. You first need to turn to the channel with Chromecast Ultra running on-screen - there you should see the usual linking code. Open the Stadia app on your phone, tap the controller icon, then tap "Phone Touch Gamepad". Tap "Play on TV" and press the linking code sequence on the virtual controls.
If you want to use a Bluetooth controller running through the phone on Chromecast Ultra, you just set up the controller instead of the "Phone Touch Gamepad" instruction. The rest is the same.