There’s no shortage of large sensors, they just don’t make sense in a phone unless you want it to be huge. In fact there’s a migration upwards in camera sensor sizes owing to the decreasing size of the support electronics, e.g. you can now get a Hasselblad medium format camera that’s smaller than a DSLR. Of course the lenses are huge.

I for one would love for Apple or Samsung or whoever to release a photographer’s smartphone with a micro 4/3 mount (it’s the only multi firm properly documented lens mount system and also seems to be the sweet spot for trading off image quality, sensor readout speed, and size) BUT the phone would be at minimum 20mm thick.