So it is probably easier to call them “normal camera / rear camera” and “selfie camera / front camera”.
I understood: When you start your camera app …
- the rear camera shows the error “Can’t connect to the camera”, you see something blurred and but there are some stripes on the screen. Right?
- the front camera works without any issue. Correct?
As explained I would try another camera app at first. → Come back an tell us the result.
If you have the same issues with another app it is probably hardware related.
You eventually need a new rear camera module then.
Before you contact the support like mentioned by @AnotherElk I would try to open your phone (it was made to do so 
) and clear the connector of the camera module.
Here is a guide how to open it and replace the module: Fairphone 2 Rear Camera Module Replacement - iFixit Repair Guide
In your case you will only check/clear the connector of the module, put everything together again and check again if the normal camera still have these issues.
If you need help with these kind of things (and if you don’t have anyone next to you), you can watch out for a community group next to you. Fairphone Community Map
Or you join a community event Current and upcoming events at Fairphone - Join us!
So next steps:
- use another app
- clear the rear camera connector to check if the current module has a hardware problem