Discord doesn't require a phone number AFAIK. I have used an account without a phone number attached for nigh on three years now.
Not that it's necessarily malicious in intent—requiring “extra verification” only on suspected misuse isn't entirely unreasonable, and that's awfully hard to distinguish from things like targeted privacy attacks—but it would be nice to establish this sort of thing as common knowledge, especially since I imagine the chaff of “huh? no they don't” is only to their benefit.
Using any form of datacentre IP or anonymiser requires phone verification randomly within a few minutes or hours of starting interaction [regardless of server].
You get a different error message and cannot use discord at all: https://i.imgur.com/T57xcff.png