Phone number is the weakest form of 2FA but it's still an improvement. I've never had to use my phone in Discord though, I don't how Discord would even verify someone's phone number as legitimate. But like I said I have a couple Discord accounts with different emails, probably on 30-40 servers, and have never run in to this. So if they're collecting personal details in this really granular and specific manner, it seems like they're not doing a very good job at it.