Hey there,
I got my FP2 this March in combination with a mobile phone contract at the Dutch provider mobiel.nl. Now my microphone is apparently broken and I would like to know if the warranty includes phones sold by third parties, and if so, if the warranty claim procedure is the same? I am a bit lost in what to do here.
Yes on both questions. Don’t hesitate to contact Fairphone Support. 
If it’s urgent, call them (phone number and office hourse on the same page I linked to).
Oh, and here’s everything you can do on your own to figure out if your microphone can be brought to work without a replacement:
https://support.fairphone.com/hc/en-us/articles/115001041206-Troubleshoot-your-Fairphone-2-issue
Thank you for this quick answer! In my phone documents I couldn’t really find what to do in case of warranty, so I wanted to make sure.
And I already planned on first checking all contacts, I already experienced how they sometimes get loose or dirty and can cause problems that have nothing to with the actual functionality of the module
Just for explanation: A warranty is always somethig offered by the manufacturer (i.e. Fairphone) and not by the vendor