It isn’t just a server thing. Discord can request a phone number from you if they think something unusual is happening. Trying to create an account while using tor will make them ask for a phone number, and they reject those numbers offered by shared number services.

Sent by me:

Dear Discord Privacy Team!

I’m writing to you to inform you that your platform (mobile, desktop, browser) can enforce the user to verify their account with a phone number, after the user has changed their E-Mail adress. This is a serios privacy problem! I’d like you to verify that you don’t intend on providing other (more privacy friendly) means of account verification apart from providing the phone number. I suddenly cannot use my Discord account due to this and I object to providing a phone number.

Kind regards, ~sntx

Their answer:

Discord Privacy Team (Discord Support)

Hi there,

Thanks for reaching out to us. Unfortunately, we aren’t able to assist you here. This channel is reserved for privacy questions and requests.

It looks like this is a question for our Customer Support team. We recommend that you resubmit your request and choose the appropriate reporting option. You can do so here: […].

In the meantime you can check out our Help Center for more info on everything Discord.

We appreciate your understanding.

Sincerely, Discord Privacy Team