You can use a hardware security key, like a yubi key, or a software fido2 equivalent.

That way it satisfies the two factor requirement, without using a phone number.

For initial registration you can use an SMS service like SMS pool or the others, you pay a little money, you receive a real text message to a real phone number. You just don’t have access to that number in the future

Your voice, vocabulary choice, lighting conditions, power interference frequency, can all give away parts of your location and identity. You have to choose what level of paranoia is sufficient

The most anonymous, would be to have a v-tuber like model, respond and parrot LLM generated voice audio, from a script that’s been translated a few times. Or pay a voice actor from Fiverr to read your script.

Of course this whole time, using a VPN.