A phone is not where a shot gets finished, and a page that pretends otherwise is wasting your time. What it is good for is the half of animation that is judgement rather than construction: does this move read, is the timing right, does that hold last too long. You answer those by pressing play — and pressing play has never needed a 27-inch display.
So Studio's phone shell is built around that loop rather than around a shrunken desktop. The viewport goes full-bleed, panels become sheets from a dock whose contents change with the section you are in, and the Animation section opens straight onto the dopesheet with Set key and Auto within thumb reach. Playback and scrubbing sit above the dock instead of in a desktop transport bar, because on a phone the timeline is a sheet with nothing above it — the controls had to move to where the hand already is.
Everything here is the real application, not a companion. The keys you set on a phone are the same keys, in the same document, a desktop reads; the curve editor is one switch away at the top of the same sheet; and the scene is stored in your Mixos account, so there is no export step between the phone and the machine you finish on. iPhone runs portrait only, deliberately — a landscape 3D timeline on a handset was worse than not offering one, and that is a decision rather than an omission.
The boundaries are worth stating plainly. Detailed modeling, lighting and a long path-traced render all want a bigger screen and more GPU than a handset brings. There is no cloth, hair, particle or rigid-body solver anywhere in Studio, and no production character rig. And if you own an iPad, it is the better tablet-sized answer — in landscape it keeps the full desk layout, rails and all. The phone is for keying, retiming and watching it move.