I've been able to play it on my phone again thanks to a closed alpha on the GeForce Now cloud gaming service, but it hasn't been available on the App Store. This loophole works a lot better than I expected, and it's not quite as seamless as using a native app.
You will be playing a mobile-optimized version of the game with this closed alpha. The experience is well-designed for touch, with easy-to-navigate menus and large (though finicky) onscreen controls. I've played most matches with my phone plugged into my Backbone One, and the GeForce Now version also supports controllers.
I haven't had any issues with the responsiveness of the game, it feels like I was playing on my Nintendo Switch or PS5. Your internet connection may be a factor in your mileage, and I might have just had a string of good luck. I didn't feel like the fact that it was streaming from the cloud hindered my ability to keep up. The biggest complaint I have with playing on the service is that the screen on my phone feels too small, and that's probably because I'm using a mini phone.
Until Apple allows the native Fortnite app back on the App Store, it's an excellent way to circumvent it. The turn-based card mechanics of Inscryption don't require any twitchy movements that could be affected by lag, and that's the only other experience I've had with GeForce Now. This version of the game I've streamed from GeForce Now plays as if it was installed on my phone, and it's much more action-heavy, requiring fast reflexes and quick thinking.
It's not clear when this version might be available more widely. You have to request access to the closed alpha, and admission isn't guaranteed, according to the website. If you've been wanting to jump onto the newly flipped Fortnite island on your phone, you might want to sign up for the closed alpha. You will almost certainly be waiting longer for the native app to come back to the App Store if you wait a while.