My friend sent me a Boss PH-3 phaser to fix, not knowing it was digital. I don't know much about digital circuits, unfortunately.

The problem seems to be with the knob all the way to the right, the "STAGE" knob. For all settings, except the "4" setting, it sounds like it's in "STEP" mode, this weird computery sound-effect. See demo of STEP mode here at time 1:30
My guess would be that this is simply a problem with the STAGE knob itself. However, I don't even know much about digital selector knobs. Where could I get a replacement? Is it easy to replace, or will it involve some crazy SMD stuff that I can't easily solder?
Strangely, here the STAGE knob looks like a normal potentiometer:
https://www.audioservicemanuals.com/b/boss/boss-ph/329737-boss-ph-3-phase-shifter-schematicHowever, the knob is definitely quantized, with discrete clicks along the way. How do these sorts of digital selectors work?