A phone can be a vital accessory for a cyclist, so why not keep it charged up at the same time? The MAKE team details how to build a bike-powered phone charger in this easy-to-follow video.
As you can see in the video above, you'll need to be comfortable working with electronics, but if you know what you're doing, the video is pretty easy to keep up with. The finished product is clean and unassuming, and would be awesome to pair with a DIY phone bike mount.
The only thing I'd change would be to plug the USB cord into a small external battery pack to act as a buffer between the generator and your phone, so it can keep charging when you're taking a break. Click through the source link for some more details if you want to tackle this yourself.