Which Fairphone do you have or are you interested in?
If i remember it right, Fairphone have shared that they wil not included wireless charging for a good reason.
The parts how are needed for wireless charging need quite a bit of those conflict minimaals and wireless charging is energy inefficient what causes residual heat which can shorten the life of the battery.
Can someone conform?
For a (waterproof) case:
i remember @Meaghan dit post about a waterproof case,
i will add the link here if i found it:
added:
if you still like to have wireless charging maybe this is a option for you?