The Steam Link app, designed to extend Steam’s suite of services and accessibility, is now available free of charge for iOS and Apple TV users.
Steam Link allows users to play Steam games from their PC or Mac through the house over the LAN network onto other devices like the nVidia Shield, AppleTV, Android phones and iOS devices.
To use the app on your iPhone or iPad you need at least iOS 10 or higher or an AppleTV HD or 4K.
You can grab the application in the AppleTV store or for your iPhone or iPad over here.