At which point is it better to just build 12 non-repairable phones instead of 10 repairable ones + some spare parts?
Take, for example, the user-serviceable battery with its thick casing. Given that you'd expect to swap it 1-2 times during the useful lifetime of a phone platform, does it need to be that easy to swap, or would it be OK to require some level of disassembly?
Not "melt the glue, pull with suction cup, pry open, disconnect 15 connectors, loosen two sets of 8 screws (all different), remove all innards, replace some single-use parts" level of disassembly, something like "losen two screws, pry off the back, loosen two more screws, swap battery" like with the Nexus 4: https://www.ifixit.com/Guide/Nexus+4+Battery+Replacement/130...
We don't complain when we take a wristwatch to a watch shop at the corner to swap the battery every few years, waiting a few minutes and paying $5-10 for the service and another $5 for the battery. I would be perfectly OK with a phone that works like that: Repairable (especially commonly swapped parts), but not average-user-servicable.
Edit: Looking at the Fairphone 3, it doesn't look as bad. I remember looking at the Fairphone 2, which looked like a brick made of cheap plastic all around.