There is an app, but unfortunately private messages don't send through it, or they'll hang and seem not to send, but send in the background.
I've looked for solutions for using LPF on mobile, and unfortunately there's no good solution.
Not sure why there isn't just a CSS sheet that could resize things appropriately for mobile. Maybe it would impair the ad networks or create a security risk - those are often the concerns.
It helps a lot if you turn on the white color scheme and turn off people's avatars and signatures. Some people use big obnoxious photos for their sigs.