Hello Richard, you are "only" connecting the audio output to the car. The phone's microphone is still used for calls. At least for me, this works well as long as I have the phone with a holder directly in front of me in the ventilation grilles. The phone may think that there should be a microphone at the other end and mutes it on the phone. You can only check this in the settings when the phone is plugged in. Alternatively, I also use a Bluetooth adapter so that my daughter can also play music from her mobile via the speakers. Yours sincerely, André.