There is a Volume controle and a Tone-controle.
Also the mix of value's are for loudness in the lower part of the volume.

Changing these values has an effect on the way the loudness is controled
and in what volume level.
Also the amount of Bass-Trebble that is changed.

You can overrule the Loundness just bij not connecting it.
The overal value must be the same to controle the volume as over the complete range.

Same with the tone-control.
It is indeed that Philips combined Bass and Trebble in 1 potentiometer.
That are the mix of value's.

EDIT;
In your case there are 2 volume controles.
Tone controle is with a 5 step switch

Then there is a switch for bandwith, Pull for wide range.
ALso a 5 times switch for quality.
3 for Pick-up and 2 for radio.
The combination of R and C's are the Loudness and tone-controle parts.

It's a bit complicated system to see the exact parts for Bass, Trebble and Loudness.

Replacing a potentiometer is take care the overall value that must be correct.
The tap is not that of a matter or just leave it not connected.
But no loudness controle is than a fact.