Same for me, and my account is almost a decade old. I think it depends a lot where are you from and the kind of activity, as i read stories of people being asked to register a number out of nowhere.
Many servers requires you to have it tho, due to spam protection. I just don't talk on those.
It’s tragic but I have the “verified” setting turned on my public server because it’s literally impossible to stop a determined spammer with the tools Discord has. They can make new accounts faster than you can ban them, and there’s no like “IP ban” equivalent
If your account is a decade old, and you registered at 13, you're now 23 and they don't need to verify you're older than 18. If you were younger than 13, they might be required to delete your account.
Each discord server can decide whether they only will allow people with a phone number on. When you hit one of those, Discord will ask you for your number.
Those require a phone for you to send messages and interact. It will ask you to 'Verify phone', but you can chose not to and stay on the server as read-only, Discord itself won't bother you about it. I am on a few like that for quite some time.