A:Answer I have the iPhone XS and a UAG Monarch Case. While the phone will fit in the Osmo Mobile 2, with the case on, the jaws don't provide the ideal clamping with the phone in the case.. but it works great for a quick insert and qo. For longer shoots, or where radical movement is required, you may want a slimmer, or no, case.
I notice that with my XS & Case installed I had to adjust the roll outward enough that there was some interference when moved manually. This interference is only evident when the unit is off and there is no problem during use (due to the stabilization reducing range of camera motion.)