I will admit the Fairphone 6+ doesn’t have the LOUDEST speaker under the sun, so it won’t light up a busy party but on any bluetooth headphones and speaker and with Android Auto I’ve not experienced any issues. The sound is adequate for a phone in its price range and not worse or better than what you’d find on any Android phone in that range. If you mean the audio recorded for video again… I wouldn’t hand the phone to Christopher Nolan and say “just use this, the audio will be fine in an IMAX theater”, but if I wanted to film a casual event, it would be absolutely fine. The camera is the camera. The sensor is actually from SONY. Again, it’s the expectations you have. It takes quite good shots under good light conditions and acceptable ones at night. VoWiFi is almost always a carrier dependent issue. I use the original 6 in the US with T-Mobile and even when we were told that it is “absolutely not intended for the US”, WiFi calling has worked out of the box since day 1.
Audio and Camera are identical between FP6 and FP6+, like most things.
The speakers are a lot worse than flagship speakers. A little bit of EQ gets rid of the tinny sound. They are not very loud and will not give you any bass but I have gotten used to it quickly. iodeOS for instance includes AudioFX as a system-wide EQ, letting you tweak speaker EQ manually.
The camera is okay midrange level when you use the official camera app available on stock Android and e/OS/. On custom ROMs you only get generic camera2 api apps (gcam for a slight improvement), which are okay in bright conditions but quite poor in low light. Expect thing like focus and HDR to not work when running a custom ROM.
There is nothing technically preventing the official camera app from running on custom ROMs, but they can’t include it in their builds due to the proprietary license. If you were to build your own rom or use root to install it as a system app, it could work.
Wi-Fi calling depends on carrier, the main blockade is the carrier specific whitelist. One of my SIMs works with wifi calling on a custom ROM, the other one doesn’t.