Discord has an account flag that triggers a mandatory phone number verification. It happens if you do things like send messages too quickly over the span of about a minute, or send multiple friend requests, or join too many servers, or start too many DMs, or indeed, join any server that is set to require phone number verification.
I am in dozens of servers and have not encountered this demand for a phone number. I have been in servers that required it for moderators as part of 2FA, and I just declined to moderate there. It had no effect on my use of any other server.
Just because something hasn't happened to you, doesn't mean it doesn't happen to other people
It never happened to him, so it's never happened
Makes this huge data leak a real head scratcher
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If it doesn't rain one day, that's not evidence there exists no rain
That's about the level of evidence that your specific user account offers to you about whether phone verification is a thing their anti-spam algorithms can trigger...
It has happened to me on two accounts. OP is also not the only other person I've seen who has dealt with it.
Bully for you that you haven't encountered it, but it's certainly a thing.
Anyone on HN should know the fickle nature of fraud detection, especially when the cost of getting it wrong is 0.