This is my take on a already well documented little project. Very simple to make and a good introduction to electronics and solar powered stuff. Works just fine too. You need to generate 5-6V to charge a phone.
You will need:
Solar panels. I used 2 panels. (3V I think )
5V voltage regulator
USB female jack/connector
Epoxy or hot glue
Step 1: Bits & Pieces
Gather together all your stuff. You need to make sure you know which side is top and which side is the bottom of the USB plug and the voltage regulator so that you solder the correct pins.
The regulator keeps the power output to 5v.