Looks like a pre-facelift W204 C-Class? If so, there's a 3.5mm jack socket in the glovebox. Unless you want to spend a couple of hundred quid on a media interface module, there are a couple of solutions but neither will give you use of the steering wheel controls to navigate your music, nor will they display track info on the car's screen. Cheapest way is to use a 3.5mm male to 3.5mm male jack plug lead and plug one end into the headphone socket of your iPhone and the other into the glovebox socket, or use a Bluetooth receiver like
this (others are available) plugged into the glovebox socket and then stream audio from the phone.