[Welsh Anorak]

As you say you have some learning to do, without meaning to be rude, could I just explain simply how your radiogram works?
The very low signal from the cartridge is fed to a preamplifier to boost the signal and 'equalise' it, which in simple terms means getting it back to the correct tone as the original. It's then fed to the switch unit where you can choose other imputs, such as the radio. This is where your phone should be connected, perhaps by 'aux' inputs if there are any. Now comes the volume control, and the chosen signal is then fed into the amplifier to raise it to a level where it can feed the speakers - many hundreds of times larger than the signal from your cartridge.
I hope this makes it a bit clearer. Well done on finding the original fault!