Setting up your phone to work through the stereo is really complicated and expensive. Basically, you have to dismantle the instrument cluster to mount a mic, wire the Becker AUX, hookup a mute switch relay, then hook it up to a 2.5mm phone jack.
I can explain in more detail if you want but I would recommend a bluetooth headset or visor mounted speakerphone, it will be easier and cheaper.
