You can adjust the output of the J-retro to match the active level with the passive. There is a trim pot inside for each pickup, so you can match them to each other, then take them both down the same amount.
Also, since your maxing your treble, I wonder if you need to turn the bass knob down. The bass EQ on the J-retro is boost only, center detent is not flat. I don't know much about phasers, but if they don't like too many lows, that could be your problem.