The main purpose of a phase is to logically group together project activities. This assists with:

• Determining what work needs to be completed
• Ensuring that all relevant stakeholders are consulted during the phase
• Facilitating an understanding of the interdependencies between phase deliverables

Project phase models vary according to industry and organization. However, most phase models contain the following key elements:

• Start-up or initiation: The phase in which the project is defined and authorized.
• Planning: The phase in which the project objectives, deliverables, schedule, and budget are developed.
• Delivery or execution: The phase in which the project plan is executed to complete the project deliverables.
• Closure: The phase in which the project is completed, archived, and lessons learned are captured.

Some methods also define an 'umbrella' or overarching phase which defines how the project as a whole will be monitored and controlled. The term 'phase' implies a sequential order. In real life Project Managers may move back and forth between the phases, particularly planning and delivery. For example, if a change request is raised during delivery the Project Manager my move 'back' to the planning phase to assess the impact of the change on the project schedule, budget, scope and quality. To reflect this the PMBOK defines process groups rather than phases. The PMBOK process groups are:

• Initiating
• Planning
• Executing
• Monitoring and Controlling
• Closing

The PRINCE2 methodology also uses the concept of phase. PRINCE2 phases are:

• Starting Up a Project
• Directing a Project (an overarching or umbrella phase)
• Initiating a Project
• Controlling a Stage
• Closing a Project

Each phase or process group includes the creation of project management deliverables and sign-offs which define the scope, set objectives, report on progress, control changes, track costs, learn lessons and close the project.