Update 30 August 2023:
After 10 years of hard research 
Fairphone can soon offer these for the Fairphone 5:
As we haven’t got a Fairphone Support article about this longstanding issue, I have cobbled together the little that is known. If you can add information, please do so, but always cite a source and make your links as precise as possible.
| Model | Driver(s) | Length(s) | Diameter | Sources |
|---|---|---|---|---|
| FP1 | Phillips #000 | 3.9 mm / 2.5 mm | ? | iFixit (steps 7 & 17) |
| FP2 | Phillips #0 | 5.5 mm | 1.4 mm | iFixit (step 6), Forum |
| FP3 | Phillips #00 (or #0) | 3.8-4.0 mm | 1.4 mm | iFixit (step 5), Forum, Forum |
| FP4 | Phillips #00 (or #0) | 4.5 mm | 1.4 mm | Forum |
For potential sources (where to buy), see these topics: