Ah- I see what you mean now
The project hasnt actually started, and you want phase 1 and 3 to move to suit phase 2?
If thats the case (your explanation is good, I may just be missing the point I'm afraid) then I would tend to change the layout slightly. Instead of using start of phase 2 to set the task 1, use task 1 as a start for phase 2, using a "must start on" constraint. Then link phases 1 and 3 from this date, using a SS relationship with a negative lag.
I have included an mpp and pdf of your project, showing your original layout and my suggested layout. Note that negative lags are generally frowned upon (by convention) but in this case I think it would be the most useful and effective way to show what you need to.
If the start date for phase 2 changes, just change the constraint date in task 1 (the phase 2 start date) and this will automatically change phase 1 and 3. The only thing I wasnt sure of was the lag between phase 1 and phase 2- I used a positive lag in the first example to set these to your days, but you can change this to whatever you want it to be by adjusting the lag to phase 1.
Hope this is helpful- if will check in a day or so in case it doesnt do what you want
NOTE mpp file is zipped, as the board doesnt accept a straight mpp (strange fo ra Project help board, but what the hey
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