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
Policies like that are almost entirely about minimizing fraud and harassment. It really sucks for people who don't have mobile phones that support authentication texts or whatever (since, even as you pointed out, the requirement is mostly a phone number) but it also drastically cuts down on fake/harassment accounts.
It's about data harvesting and selling not safety or any other mentioned.
Even Github does not require any personal information, so there are certainly other ways.
And Github is Microsoft who need those capabilities for basically every other website they sell.
Whereas gitlab is REALLY good software with... a website nobody ever really asked for but that still needs to exist to sell people that software.
This comes up with a lot of services. I think everyone lost their god damned minds when overwatch added phone verification?
Like, I don't like it. But I have friends who ahve had to deal with harassment campaigns against their products (or persons) and the like and get why you would do what, on the surface, is a pretty trivial ask as a way to remove sock puppets.
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.
Which means you likely weren't invested in engaging in a meaningful manner. That is especially important for filing a bug report on an open source project.
And I guess I just don't view a phone number as having much value from a privacy standpoint. Basically every number is compromised to the point that it is dependent on your phone/service provider to block spam. One more site having my phone number doesn't really bother me if it is a site I want to "engage" with.
Also: Never underestimate how much data is already out there just based on what pages you load. Privacy is long since dead and people do not understand how easy it is to cross reference to realize that "Jimmy in The Netherlands" is actually "Jim Stark at 101 Fake Street in Baltimore Maryland whose sister is Susie Clark with facebook username sclark_420"
User flagging works too