1. Connect the phone to the computer via USB cord.
2. Copy the files you want to transfer over to an empty folder on the computer.
3. Disconnect the phone from the computer and then connect the drive to the computer.
4. Copy the files from the folder on the computer over to the drive.
NOTE: I say copy from the computer to the drive so that you are leaving a back up on the computer. However, that is just a suggestion.