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.
You can set up a community on their servers.
I’m not sure why they chose to use misleading language, but it is misleading.
Gamers are well familiar with different communities actually hosting servers and instances for games or voice chat pre discord. Discord offers the same experience but without physically being different servers. Keeping the name guides users in the same way OSs call it a recycling bin despite not actually being a bin.
I also have trouble going along with the doublespeak. If a supermarket called their beer apple juice, I'd also not be offering my friends "apple juice", I'd call it what it is
Guild is innocuous enough and since the API docs still call their communities that, that can be a term to use among those in the know to have common and clear terminology
'Guilds in Discord represent an isolated collection of users and channels, and are often referred to as "servers" in the UI.' —https://discord.com/developers/docs/resources/guild
Focusing on the fact that it's not really a "server" because they aren't running as separate processes seems like utterly silly pedantry, and we probably don't even know if that's actually true regarding Discord or not.
It's like pretending a taxi is the same as owning a vehicle, even if the taxi company was your neighbor and there's always someone available. The result is the same but the distinction couldn't be clearer. To me it's similarly misrepresentative to say you own a car when you live next to a big taxi station, as to say the SaaS web front-end you get on Discord is a rented server
Makes this huge data leak a real head scratcher
Bully for you that you haven't encountered it, but it's certainly a thing.