Either purchase a specific MMI cable - lightening connector from Audi or ebay for £ 30-40 - Short cable that means your phone is in the glovebox
Purchase a Tune2air Bluetooth receiver (don't confuse with phone Bluetooth). This works fine unless you use your phone on standard Bluetooth and will skip sections of playback everytime you come in and out of signal.
Safest bet is to purchase a 2nd hand ipod classic off ebay and leave in your glovebox with all your tunes on, keeping your phone separate.
Hope this helps
BTW - The MMI-USB Cable will not allow music to be played from an iphone! I found out the hard way