Phases are basically different perspective of your project. Each phase will have specific goals, focused milestones and we group phases based on that.
Sub projects we must repeat all phases to have better control over projects. Dealing with each project separately meaning you have to perform initiation design plan execution control and closure to fulfill the main project goal.
Was going thru Fig 5-8 from Create WBS and I see Phases and Subprojects it fig. There is even a Subproject under a Phase. There is no mention of Subproject in Ch 2. Whats the distinction between two? Any thoughts?