Phabricator has a very particular workflows. If you use that workflow, it is really fast to use; you can do almost everything from the command line except the actual code review/approval. And it is pretty good about encouraging that your repo is kept clean, decluttered, and consistent.

Whereas gitlab/github etc are much more flexible, but also slower to use and more demanding that your individual developers adhere to your standards.

I think Phab is best for projects of 3-5 to 50 (basically until your project is dealing with multiple commits per hour and no single repo is going to be painless), especially when you have new team members and you'd rather let the the tools enforce the workflow as opposed to policing them yourselves. However, if you don't like that workflow, you're never going to be happy with Phab.

Finally, Phab has some really nice features that I haven't seen elsewhere, like posting lint errors inline in the merge request.