I just discovered yesterday that while the Discord itself does not require it in all cases, certain servers with the highest restrictions can require that you have a phone number verified with Discord in order to post.

Try it from a VPN. It requires a phone number. If you do it from Tor, it requires a phone number and like 27 captchas.

When companies like Discord or Google seem to let you create an account without a phone number, what that really means is that they already figured out your phone number based on your IP, HTTP ETAGs, or browser fingerprint.

Try it again using TorBrowser, or Tails on a VPN.