Phabricator is built by 2 people (I am the designer half of the team) so bandwidth for a mobile app is essentially nill. It is designed & built fully responsive though, and light on the wire. You should be able to use the web version on your phone with no issues.
Hey Phabricator dev here, would love to see you take a better look at Phabricator as well. I'm not sure that we really "do too much" as our product is guided mostly by the tenants of code quality and developer efficiency. Specifically we feel it better to have these tools all integrated so developers spend more time just building features. Some basic overview for code review would be:
Hard to say since every tool out there moves very fast and we're just building what we think our users want. Overall my personal opinion is the "pull request" model is flawed for businesses but great for open source. Phabricator doesn't serve two masters in that regard. This means we focus more on developer efficiency and code quality. Tools like arcanist are harder to convince people to adopt, but save me personally a few hours each week. (Arcanist does pre-commit lint, unit, and patch emitting). Other tools like Herald (business actions!) and Owners (claim you own code!) are also highly useful at scale.
Not sure what you mean, I've always billed it as an internal tools platform since it's our intent to have it do everything you need. (bugs, repo, review, kanban, wiki, chat, etc)