That's peculiar. I run a couple of big Discord servers and never heard anyone saying they have problems logging in.

First about 18 months ago they said I had an IP phone and could no longer log in (my carrier is Republic Wireless). When I contacted support and told them that I had been able to login with that number in the past they basically said "we're tightening up security, too bad so sad. get another phone number" Then recently I found that I was able to log in when I wanted to try midjourney (Republic changed something back in April, apparently so they it no longer looks like an IP phone#). Then I wanted to login to discord on the my desktop and it gave me some weird errors which basically amounted to "this number is already claimed" (it was, by me) so now I'm back to ignoring discord again.

Yeah, the phone # requirement renders Discord a non-starter. There is no benign reason why this type of service requires a telephone number.

Bots and spam.

That's because they couldn't log in to complain. Recreating the broken contact form effect.

They are servers for forums so that would be the natural place to complain.