Discord doesn’t require a phone number. It’s individual community owners who opt to require it. You can create a server that doesn’t require one but it effectively means you can’t ban people since they can just sign up again on a new account.
I refuse to use their “create a server” language. It is not a server by any definition of the word server.
You can set up a community on their servers.
I’m not sure why they chose to use misleading language, but it is misleading.
Discord has an account flag that triggers a mandatory phone number verification. It happens if you do things like send messages too quickly over the span of about a minute, or send multiple friend requests, or join too many servers, or start too many DMs, or indeed, join any server that is set to require phone number verification.
I tried making an account once, technically my account was created but trying to log in only gets me a screen that requires I verify a phone number. I was never even able to attempt to join a server. I assume it's my browser's privacy settings and ad blocker but I'm not sure.