I've never owned an iphone (and have no intention of ever doing so) so I can't speak from direct experience, but I would heavily bet that a far easier path would be to use the Steam Link iOS app to connect remotely to your gaming rig (and to be clear, a Steam Deck works just fine as a gaming rig if you don't have a bigger PC you'd prefer to use). If you're on the same LAN, performance is good enough that you may not even notice it's not running locally.
Wireless VR and Stadia are both insanely impressive. Think about how much data you've gotta be moving (and how quickly) to have an 8k video stream feel smooth, or have a game computed in a data center feel local.
UTM for iOS has been basically neutered on performance so I doubt it would even run. The authors even had to rebrand it as a "retro OS emulator" because it can't run anything newer than XP.