You are right, I didn't get your answer the first time. You suggested to make a document of every Chapter. My first reaction to the question was to make 4 different phase documents. In that case you will have to copy some chapters from one phase document to an onter.
The whole idea is to leave all on one document en simply collapse (close) the chapters you don't need to fill for that particular phase.

Than you still have only one document for an project instead of 21 (if I split the document on the chapters).

I thought the idea is simple, make an multiple choice field (Phase 1 till Phase 4)
Then hide/collapse all the chapters that are not needed for that Phase. Clean and simple.

Can you put me in the right direction for that?
Thanks.