Tor is not possible, I actually started with tor but I had to change it because webrtc is disabled in tor browsers.
Is there any alternative for webrtc that could work with Tor?
WebRTC is most popular protocol though, i doubt Tor Browser would support protocol alternative which barely used anywhere else.
I agree tg, signal, matrix are all more convenient but basically now we have an alternative p2p network (Lightning Network) that has payments built in. Even though those platforms will do end to end encryption, there will still be some central servers that arrange the call, help with discovery etc.
No central servers for phone conversation can be a absolute game changer in time of censorship.
I think that tox.chat is not using any centralized servers and it is open source software, but there are not payments built in.
FYI, Matrix protocol is federated/distributed, not centralized.