This is one but not the only case discord uses mobile numbers. If for any reason discord figures you are a probable source of spam - they dont tell you the criteria for that for obvious reasons - discord will present you with a prompt to verify with a unique mobile number. They only tell you so after the normal email signup and the profile will be instant locked. So you are locked out on profile not on "server" level. For people not on discord: A "server" is something like a subreddit or a part of discord which is subadmined by a certain group/admin. The thing is whatever they exactly do it can flag you for any reason, not only if you really spammed the platform and they seem to use rather creepy technology to make the flagging sticky. At least flushing your browser profile and changing IPs is NOT enough to remove it, so they might be using TLS supercookies, screen resolution or whatever. Would be intresting if some privacy researcher reverses their tracking tech. I had that happen to me in the past and cant tell you what exactly caused it. It may (and equally likely may not) have been caused by an account of mine being thrown out of a "server" after pointing out some lets say inaccuracies that our student government spread. (I didnt spam the server. But it contraticted some talking points they rather not want contraticted.) This wasnt a platform ban either just a local admin action, but it teached me you really want seperate identifiers for different tasks, especially if you somehow engage with politics, cause otherwise crazy people will start following you around and discord makes it easy to track you across servers. You would probably run into the same issue if you engage with health related, nsfw or really any non mainstream content. Other reasons discord might figure you are a likely spam source might be use of a vpn or a network range they already have seen spamming. I cant tell you if they also just want to collect numbers, a blog post of then claimed they only do so to combat spam and not for advertising. At least in germany mobile numbers are tied to your real identity: To get one you have to provide ID to the mobile provider so the goverment has an easier time to spy on you if it wants to. Also you can be followed between platforms with the number. For example you would be able to find me on signal if you had my number. There are ways to firewall against this by using virtual mobile numbers (google voice or something) but they can be detected, it is work and Im not sure if they are allowed or blocked. Lastly, at a certain point you can only join so many "servers" with a free account, which will be quickly reached if every damn software project out there uses one. Though I think this is fair from discords POV. I mean in the end they need to make money somehow.

Im aware of that and dont have a solution for that. Its not my job to provide one. The thing is there doesnt need to be one if you just document your stuff in a normal way. Also other platforms like reddit face the same problem and seem to be able to solve it in another way, so its not mandatory to survive in the net. Spam has always been an issue as long as the public internet existed. There are other ways to deal with it than introducing global identifiers which can be correlated between platforms and the "real world".

That's shortsighted. GP doesn't want to share their phone number, because then that phone number is likely to be sold together with their other data which can lead to more nasty problems.

That's not the only alternative. You see these kinds of intrusive checks on platforms that have drastically under-funded moderation/safety teams. I don't know Discord's numbers, but Twitter's total revenue pre-Musk was about $1/user/month or about $0.01/tweet. Plus there's a hunger for investor-beloved growth metrics that leaves things biased toward greasing the signup funnels. So you end up with privacy-destroying compromises like this.

The solution would be easy: at least offer an alternative. I would gladly give you a few cents or a dollar so you leave me alone with the dishonest bullshit. Probably one of the easiest and most effective ways you could use to fight spammers, but it is obvious why nobody does it or offers the option, because they want numbers. Would be nice to at least stop the charade.

In short, no, the alternative is not "being overrun by spam".

Documentation

HTML files. Or a PDF.

Nope.

Discord sometimes flags your whole account to require a phone number.

It's not a "server"[sic]-specific requirement that can be disabled somewhere; it's an account-wide requirement that cannot be disabled unless you open a support ticket and pray that the person in charge of your ticket is not having a bad day.

I might have gotten unlucky with my ISP, but Discord blocking me from doing anything at all unless I give them my phone number, is what made me leave it once and for all.

Oh but without deleting my account, because I can't delete the account unless I give them my phone number.