This idea has been merged into another idea. To comment or vote on this idea, please visit A-I-8519 Ability to filter based on phase and milestone characteristics in Gantt chart.
The current Gantt view only provides the functionality to filter the view by Release/Initiative/Goal/Workspace. I would find it incredibly useful to be able to filter Phases and Milestones by completion status. When planning future work, we want the view to be as concise as possible and we don't need to see the completed Phases or Milestones.