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Agreed lags are not the best way to do this (as I said before). For an alternative, you could relink phase 1 to phase 2 to phase 3, and then set the constraints on all phase 1 tasks to "as late as possible". This would mean that phase 2 to phase 3 would be a normal dependency (occurring one after the other), while the constraint would push phase 1 to its latest possible start, which would be controlled by the phase 2 date.

Its probably easier to do than to explain, give it a try and see if it gives a better result