Does the car have a Benz phone already installed? If yes, all you need is a Blutooth puck in place of the old set and you're ready to go.
If not, you first need the Benz phone installation kit installed. That phone icon you see on the centre cluster just means that the vehicle is prewired to accept the phone kit. It does not mean that a phone was installed. A phone installation was a dealer option/accessory.