I just deleted my first reply, as I think I misunderstood your question

As I understand, you want Phase 2 to start on a fixed date, regardless of when the preceding activities end? Best way to achieve this would be to put a "must start on" constraint on the first task of phase 2. This would lock it in place, regardless ofwhat other phases do. If the start date for phase 2 changes, simply change the constraint date to the new one. This should keep the milestone (Pick up point #1 consistent.
Of course if phase over runs or phase 2 moves back, phase 1 will show a negative float, as it is constrained by Phase 2 (as I see it). However this would highlight less time for phase 1, which would have to be manually adjusted anyway.