Video calls rely on your browser, so it's key to have your browser be up to date:
For mobile, Safari updates are bundled with iOS updates. Apple doesn't update Safari with every iOS release, but when they do, they give it the version number of the iOS version it first ships with. As of summer 2019, Daily.co works with iPhone with iOS 12.01 or newer You can join Daily.co calls on Chrome, Firefox, Safari, iOS Safari and Android Chrome. (Edge is limited to 1:1 calls.)
It's strongly recommended you update to the latest OS for your device. And not just for video calling reasons — we say that for simply security, across the board.