You can download an iso file from www.ubuntu.com, and almost any other linux
website, but I doubt if it would run on a phone. Its just too big. A netbook
version would be the closest match.

The next version of Ubuntu, due out sometime in October, will support
touchscreens but that won't help much. Why? well that iso contains a lot of
software that definitely isn't usable on a tiny screen, like open office.

It is possible to customize your own version of ubuntu and you could then
cut out all but the bare core and redesign the gui. However, that's
something for the very advanced user.