Do not use the first Task to define the Project Start Date Project always calculates from Project Start (Finish) Date Schedule from Project Finish Date Option in an early planning phase:
If you change one of these variables: Task is set to:Project then calculates:
Phase 2 Phase 3 Phase 1 Project Black Box Project Start Project End
How to define Black Boxes? How to set up Dependencies?
Recommendation
Only End Milestone has no Successor
Who knows the movie Highlander with Christopher Lambert? There can be only One! One Task – One Resource!