I would also even more decrease the sub-categories*, and make category names shorter. The latter would result in (in many cases) expressive category slugs:
- Discuss (super-cat for everything else)
- Fairphone
#discuss:fairphone(both products and company) - The Forum
#discuss:the-forum
- Fairphone
- Participate (super-cat for all other projects)
- Local
#participate:local - Development
#participate:dev - Do It Yourself
#participate:diy - Beta
#participate:beta - Fairphone Angels
#participate:angels
- Local
- Help (including guides)
- FP1
#help:fp1 - FP2
#help:fp2 - Guides
#help:guides(rename to make it clear that individual issues in respect to [any OS] still go to one of the other Help sub-categories).
- FP1
- Buy/Sell
If we see the need for more #discuss sub-categories as we go, we can simply add them later. 
* I’m referring a bit to @Chris_R’s minimalistic model:
Especially the two “discuss” categories he envisioned are perfectly enough IMHO, for the moment.