I love this idea. Phobos is weird. It has and extremely low density (prompting some scientists years ago to colorfully speculate that it was a hollow alien spaceship!), it orbits Mars in a very lowretrograde orbit (atmospheric tidal drag is slowly dropping it, and it will impact Mars in a few million years), and it is heavily cratered with a whopper at one end. It's almost certainly a captured asteroid, and is worthy of further study.
Update: Phobos is not in a retrograde orbit; but it is so low that it orbits the planet faster than Mars rotates, so from the surface it appears to go backwards in the sky -- that's what I was thinking when I wrote that. Thanks for the commenters who pointed this out.
Update 2: Sigh. Reader Alan Harris pointed out it's tidal drag, not atmospheric drag, working on Phobos and dropping the orbit. D'oh!