Fault on Sony Radio/cd Player - Ford focus ghia 06 plate?

Hi
I have a fault that is constantly on the display saying 'PHONE' Obviously there is a mute button which says 'phone' but i assure you this is not the fault.
I can still operate the menus etc. but no sound. I have disconnected the battery to reboot it, with no effect. I also have to turn the radio off when i remove my keys from the ignition.
Please help, its driving me insane.