Pyrrho, what is the selector switch? Is it in any of my pictures at
Records - Home?
The selector switch is the control that selects the input (i.e., the phono, the tuner, whatever). From your second picture, I see that your unit calls it "Function." If that control is dirty or corroded on the contacts for the phono input, then it might behave as you have described. There are, of course, other possibilities, but it is what I would look at first.
Since the radio works, you know that the speakers are okay, and so is the power amplifier (the part that drives the speakers). It is a question of whether it is something in the phono section, or in the preamp section at this point. The selector is part of the preamp section.
If you do not have any DeoxIT, you can play with the input (in your case, "Function") control, turning it back and forth and seeing if that has any effect on what you hear. If it does affect the sound, giving more or less "static", then it is likely that the control needs cleaning.
Your description really fits well with the control being dirty/corroded, though, again, it is not the only possibility.