I did try on phone, laptop, and desktop. I didn't try with another email. Perhaps the channel required it, but since I was only trying to join Discord for that one channel, it wasn't worth pursuing further. I sought and got support for my issue in other places.

If discord ever decides that your account is "suspicious" (they won't tell you why they decide it), you will be completely locked out of your account and you can not do anything on the website unless you provide your phone number for verification. I have one such accounts too that I created for joining the community of a certain game. These are the only two screens you can access on this account:

They also helpfully tell you that you can only verify a single account with your phone number, so if I wanted to verify this account for a gaming community, I would de-verify the account I use for work, so I'm not going to do that, lest it looks "suspicious" to discord and they delete my account - For example a while ago the person who created one of the discord community "servers" we use for work got their discord account deleted (discord wouldn't tell us a reason).

The point isn't to bash the discord company or service, I'm just stating things that happen if you choose discord.