You've removed a lot of what looks like a timing cap and hysteresis
from the circuit. Why?
What is the truw phase relation you need, and if you have consistency but
skewed, can you make that up somewhere else (like a one-shot down the
line, before whatever it's supposed to be triggering)?
Way back in the day I used simple blocking cap, reset resistor and comparator
scheme for SCR based AC-DC motor control. Not 3-phase though, I don't know
what you're trying to do here. What is the true phase relation (mains -> trigger)
you are looking for? True zero needs either a lead network to comp the time
delay through the detector / gain, or 360 minus a smidgen of lag. A motor
control might not care so much as near zero turnon doesn't give you any
power and may cost if you connect to a line that's lower than back EMF in
the moment. We used the C-R network to get trigger at "peak or later"
(back when nobody but the power company complained to you about power
factor).