Yes we want trustworthy software and we have to assume that Fairphone does their best in this regard. But a physical switch is a protection from malicious hardware (or firmware).
I would only argue for one physical switch - to power off the cellular modem (baseband processor) because that is a proprietary system that runs proprietary software. This part of the phone has network access and often direct access to other parts of the hardware.
@m4ur1c3 mentioned that the cellular modem on the FP2 and FP3 is not well isolated but I don’t know the details.
So using an isolated modem that doesn’t have direct access to the microphone, memory, GPS,… would solve parts of those concerns.
As the Airplane mode was mentioned: do we have any confirmation, that the devices really doesn’t do any communication in this mode? Did anybody ever check or is there a statement from the manufacturer? Searching around I found a comment here:
“Airplane mode” is essentially and AT command sent to the baseband to disassociate and go to sleep, it doesn’t disable the baseband CPU, DSP or anything else.
I’m on Wi-Fi 95% of the time and do all my regular communications “over IP”. So for me it would work to just enable cellular once a day to receive some SMS and enable it once a month when I need to make a legacy phone call.