There's already a way to mount your smartphone to a Steam Controller

Mechanism Mechanism, the company behind a "gaming pillow" for the Steam Deck and a growing list of grips for handheld consoles and PCs, already has its first Steam Controller accessory ready. Valve's new controller will be available to purchase on May 4, and that same day Mechanism will start selling the Basegrip for Steam Controller, an accessory that will let you attach the controller to a smartphone and plenty of other mounts the company already sells.

The Basegrip for Steam Controller is contoured to fit snuggly over the back of the controller while leaving room for its magnetic charging puck to still attach. And because most of Mechanism's accessories are designed to work together, with the Basegrip attached, you could connect the Steam Controller to a large number of the company's existing mounts, including a phone mount that lets you magnetically attach a smartphone to the top of the controller. With a phone and controller together, you theoretically have a little handheld console for playing games.

Or, well, you could, some day. Valve has been fairly clear that the Steam Controller is only designed to work with Steam and the Steam Link app, which is why Mechanism notes that "the controller doesn't work across all of iOS or Android yet." You could use your smartphone, Steam Controller and the Steam Link app to stream your PC games, but you might struggle to play more than that. Future software updates could improve support, but it does make using the Steam Controller with a smartphone right now a bit less useful. That shouldn't detract from the other accessories Mechanism offers, though, particularly its planned Steam Controller Dock, which proudly displays the controller when you're not using it, and incorporates its charging puck to keep it powered, too.