If your IP (and possible your browser) looks “suspicious” or has been used by other users before, you need to add additional information for registration on gitlab.com, which includes your mobile phone number and possibly credit card information. Since it is not possible to contribute or even report issues on open source projects without doing so, I do not think any open source project should use this service until they change that.
Screenshot: https://i.ibb.co/XsfcfHf/gitlab.png
I don’t think having my real life phone number tied to a website or game account is a trivial ask. I’d like my data to be private, especially something as real-life and tangible as a fucking phone number. Sure, there are ways around these things, you can get a fake phone number for cheap (or possibly even free), but that’s rather more effort than I’m willing to put in for most things. If I need to enter a phone number to sign up for an account for something, chances are very extremely good I’ll just decide I don’t need the account that badly. I don’t think I’m alone in this.