A phone cradle, BUT they dont do them for modern phones ie phones from 4 years ago. The easiest way is to connect your phone via bluetooth. When you turn on the ignition do a search for bluetooth devices on your phone, passcode is 1234. The Audi bluetooth is only discoverable for a few minutes, so if you cant find it turn the ignition off then on and try again
EDIT
If you get a phone which fits the cradle it will also charge the phone, but most people just connect via bluetooth. Once paired the phone will automatically connect once the ignition is switched on, as long as you choose to authorise the Audi on your phone