Yes, I have integrated Phabricator for code review. It's awesome!
Yes, in Phabricator is possible to create a revision, you review the code in Phabricator, comment to the code and ask the submitter to recheck his code if you find errors, and only when you accepted the revision the submitter can push the code to the repository. This is just one workflow. Phabricator is flexible and can adapt your workflow really nice. It can be super configured and more, it's open source and you can write your plugins.