Many projects, such as renovations, proceed in phases, each representing a distinct time period in the life of the project.
Revit tracks the phase in which views or elements are created or demolished. You can use phase filters to control the flow of building model information into views and schedules. This allows you to create phase-specific project documentation, complete with schedules.
You can apply phases to schedules. For example, in a large renovation project, a door schedule would usually list all doors created in the project. In a building with hundreds of doors, the schedule could become difficult to work with, because the demolished doors would be listed with the post-renovation doors. Instead of working with a schedule in which half of the doors are eventually demolished, you could create one pre-demolition schedule and one post-renovation schedule, applying the appropriate phase to each.
Video: Phase Status
The following image shows a floor plan in different phases of a project: 
existing construction, 
demolition, 
new construction, and 
complete.
