Manual Phase position for Stage Fright

[GoldenPotus]

Hey guys, building a stage fright and I'm think it would be cool to have manual control of the phase position like you do in an EHX Bad Stone. Maybe expression pedal controlled too? I've build a few pedals but as far as designing/modifying circuits I'm a novice, so if anyone can help me on where I'd start that'd be awesome, thanks!