Honestly, I don't remember how I did register on Discord, but yes, you need an account. Not sure the phone number is required, by the way.

Edit: Indeed, I checked, you can use your phone number OR your email

To be honest, I found this yesterday: https://community.wolfram.com/groups/-/m/t/1472615

But it's unofficial and not very widespread. I joined the server and asked a couple of questions, there were a few active users and I didn't get the answers I needed, but maybe it will improve with time.

Here it is, I hope it will help, by the way, should anyone know any other [un]official Wolfram chat channel, please, post it here =)

Regards.