Well, I'v been repairing electronic equipment for 29 years and own, well, my sigline tells you that I own an XF capable of telephone interface too! Let's see what I can come up with.

I have never tried to interface a telephone to my sound system, but it SEEMS to me that the sound system is powering up either with the idea it has a phone connected OR in a mode where it's looking for the phone and not finding it.

PROBLEM: In my owner's manual, it TALKS about the phone interface, but tells me NOTHING about how to connect the phone to the radio, so I can't tell you where to look to see if an interface cable has been left plugged in - which COULD give the radio the idea it has a phone connected.

IDEA ONE: There is a cable plugged in, left over from a previous owner's phone, that is telling the radio to expect a phone and the radio is TRYING to tell you that it expects a phone but cant find it! If I can find where this plugs in, I'll tell you and you can look and see if it's there!

ANOTHER IDEA: Perhaps there is a menu option in the radio that is turned on (making the radio expect a phone) that can be turned off.

Sadly, I don't know what manual(s) to look in to find answers to these questions, as I am a new owner with the usual owner's manuals and a downloaded service manual (that I have not been able to find this in, I was thinking of connecting a weather radio to this input, but again, have not really attacked the project full force).

Gimme a day or two to look thru the service manual and see if I can find anything.
Or.... as is often the case, within 24 hours, SOMEONE is gonna jump in here and tell you how THEY solved the same problem!