You can use Signal desktop - all you need is a phone to receive a confirmation text message, but that needn't be a smartphone.

Even that is too much to give to a chat application. In most cases a phone number is tied to a person, requiring that is pretty much requiring a full name.

I guess one could sign up with a Google Voice number or something, but the whole idea of requiring a phone number for anything not related to a phone is just ridiculous to me.

Even more ridiculous when Walmart almost wouldn't sell me tires because I didn't have a phone number. It took three different managers to figure out how to put in 000-000-0000.