Plug the iPhone in via USB in the center armrest. Press the speaker shortcut at the top of the CUE screen to bring up the audio screen, then touch the "Media" icon near the lower right to cycle between media sources (USB, SD card, CD, etc). When the iPod appears on the screen, it will take about a minute for the CUE system to catalog and sync all your information, so voice commands and the "browse" button in the upper left may not be immediately available.
Once they are, you can press "browse" to scroll through your artist, genre, song title and playlists just like on the phone itself. You can also use voice commands such as "Play artist _____" , "play song ______" or even "playlist ______" .