You'll need a way to connect the power you generate to your phone.
Look for an old phone charger you might have, and cut it in half. We just need the piece that plugs into the phone. You could even use a USB charger cable like the one I found.
Inside the cable you should see 4 wires. White, Green, Red and Black. The Red and Black ones are the only ones we'll need for this project.
Note: For this project I used an old Blackberry Pearl. If you are using a smart phone, the white and green wires may need to be shorted out or connected to a "dummy load" to get a successful result. (I haven't tested this method yet but have had feedback from other viewers suggesting this is the case)