Component manufacturing and placement accuracy/precision
Simply said - should all the cameras of the exact given model be physically same (both dimensions and placement of lens vs sensor) than a single calibration (or say an average from 10 calibrations on 10 various phone pieces of that same model) should be enough for the rest of the crowd (1000s of users) using that model.


So,  first of all, I doubt you'll be able to figure out the exact given model – just because two phones look identical on the outside doesn't mean all the components inside are the same. Such phones are manufactured in large numbers, and supply for some of the components needed will be, by a skillful supply management, eventually be switched over, if economic or availability reasons require it. 

Then: while I'd indeed expect the manufacturing tolerances of the opto-mechanic aspects of the cameras to be very close, these are not devices sold as calibrated camera systems (as you'd buy them if you were e.g. someone strapping a CV system onto a car). So, the manufacturer won't be spending calibration time on the cameras, and they will somewhat differ. 

Then, the camera is somehow fixed inside your phone's enclosure. There's a range of ways of doing that: Gluing the camera to the case, soldering it onto the main PCB, connecting it with a flex cable, fixing it with elastic bands... So, that placement is absolutely not going to be as reliable for different models.

Then: Even if this works, you'll need to implement a calibration routine for one phone. The nice thing about software is: it inherently runs on all compatible computers, so you can run the same calibration on any phone. "Community Project" means that you can probably set up some calibration rig where you just strap your phone onto a well-defined holder, and then calibrate against your calibration target, get e.g. an OpenCV camera distortion matrix, and be done with it within seconds. And then, you'd be able to support any phone with sufficiently good camera!