iPhone 12 mini weighs 135g, over half the 250g limit for mini-drones. It seems unfeasible for a pocket-size drone in the near future, unless the drone could pull power from the iPhone and not need its own battery.
Mavic Mini has a payload capacity around 180g, but it also has a nice camera already.
Drones need power FAST for short bursts (aka one flight). I don’t know if the iPhone battery supports that usage. It would be cool though if the phone could be a truly universal tool like that.
I'd be pretty worried about an accident that damages my phone; I don't think I'd want something like that. But I wouldn't be surprised if some people do.
The pocket drone needs a way to know where you are in order to direct the camera at you and come back at the end. Right now they do so by pairing the drone with your phone (I guess using Bluetooth).
Tracking via Bluetooth would be much less trivial than "Ok, I'll fly toward that smiling face until I see a hand in bottom camera, then I'll just start descending until it looks close enough to shut down my motors".
Not that I think it should be done, but since the drone is carrying the phone, you could have the phone save a GPS point of where you are standing, and then the phone guides the drone away from that point to photograph toward it.
Depending on GPS accuracy in the phone it could work well. GPS waypoint missions are already well established in the drone world.
an actual FPV flight hobbyist 5" prop size class quadcopter (such as you might fly with goggles and a real remote control) can typically carry a gopro hero8/9/10 but a gopro is also a lot more compact, brick shaped, rugged, and has very extensively researched video stabilization systems in gopro's proprietary "hypersmooth" which writes the stabilized video into the HEVC file it records.
putting something flat and large like an iphone on a 5" FPV quadcopter would be awkward and bad.
Mavic Mini has a payload capacity around 180g, but it also has a nice camera already.