This is a fork of the A1 theme from Redmine CRM which adds a mobile layout (so you can use it on your phone).
Not all pages have been optimized so far. But I promise I'll look at every pull request.
Just try it out! No? Okay, here's quick a screenshot (not actually from a phone though):
As you can see, especially the navigation has been optimized (almost same effect happens when you press the icon in the main navigation).
Copy it to public/themes/ and activate it. You may also read the documentation.