The USB connector in my car (Honda Accord) requires the source to be formatted a specific way. That process didn't work with my Android so I'm not expecting it to work with my iPhone, but I'm going to try anyway.
Sounds like you are trying to do Bluetooth. If you radio has the capability to do streaming audio then I would suggest unpairimg your phone and starting over. If your radio does not support Bluetooth streaming you will have to use either an aux or usb cable.