The Librem phone is still years away from release – the biggest concern I have about my phone is that my mic can be hacked into and every word I say when its around can be recorded without my knowledge. It doesnt matter if im running a regular rom with gapps installed, or even AOSP with all open source software – there are backdoors that can be compormised.
That being said – I would be pretty fine with my phone as it is as long as I could hardware disable the mic when its not in use. My optimal phone would have a slider, much like the iphone one that sets it to silent, only this would hardware disable the mic and cameras.
I would be interested in trying to make my own, when when make a dongle is plugged into my usbc port, it completes the circuit and the phone and camera are connected, and when i remove it the connection is severed and they cant function.
I guess the last and worst option would be to open the phone and physically remove the mic, and then only use bluetooth or 3.5mm mic when you need to use it as a phone.