A project manager has begun a complex oil refinery project.

The planning phase is the stage where detailed project planning occurs, including the development of schedules, timelines, and milestones. According to the PMBOK® Guide, during the initiation phase, the project manager works with stakeholders to define the project at a high level. Concrete dates for the most important project milestones are typically established during the planning phase, as this is when the project’s scope, activities, resources, and timelines are defined in detail12.