Try to register a new Protonmail email address normally and you can do so without supplying too much information. Try to do so through Tor, and you will not be able to proceed without “verifying” the account with a phone number. This pattern (they want either your IP or a phone number) tells me they’re likely interested in tying accounts to real identities and shouldn’t be trusted with anything private. I would even go so far as to suspect Protonmail of being a honeypot. Oh…I’ll just leave this here:
https://privacy-watchdog.io/truth-about-protonmail/