Reviewing cameras and lenses sounds like a dream job, but it can turn every frame into a test, not a photograph ...
Especially when using the default iPhone Camera app ... The numbers used to determine ISO values -- 50, 100, 200, 400, 800, 1600, 3200, 6400, 12800, and 25600 -- were originally established ...
One issue the camera does seem to exhibit is battery drain ... ISO performance starts to drop quickly above ISO 6400, but for astrophotography, you shouldn’t need to go anywhere near this ...