BACKGROUND:
Let's say you had a bunch of acoustic drum tracks grouped together. Phase locking them is obviously necessary. I won't get into the reasons, but they have to do with fact that every microphone is also picking up stuff that other microphones were pointing towards. There's a bit of hihat on the overhead mic and vice versa. And so on...
So if there is a simultaneous tom hit and snare hit, but they are 20mS apart from each other, they will always stay 20mS apart from each other even as all drum tracks are sliced, quantize, stretched (since they are edited TOGETHER, in lock step with each other).
If the tom track was moved independently compared to the snare track, then the bleed of the tom on the snare track would not match the timing of that very same tom on the tom track.
PHASE LOCK: OFF?
So if you realize WHY one might want tracks phase locked, it makes sense to NOT phase lock tracks for which there is no bleed between them, and that you want to Flex each track within the group to its best location unto itself.
By the way, in some cases there can be interesting results (even improvements) by messing with the timing relationships between tracks with bleeding between them.