Ford 6000cd radio intermittently stops & displays phone?

Ford 6000cd radio fitted to 2008 Fiesta stops playing radio & then displays "phone" unable to return to radio or cd or aux.I have found that by depressing on/off button for at least 15 seconds will eventually return unit to standby showing date & time.Are there any buttons to be pressed in some form of sequence to reset this fault or is it for the professionals to look at ?