In this video, you will learn how to use Scene States. For clarities sake, they are essentially layers in lots of other modeling programs you are used to. They function similarly too. They allow you to change the visibility of objects in your Twinmotion model and freely change from one state from another to change this visibility. They can also be used during videos to show a progression of additional or removal of building elements. Phasing works similar to videos in that you can show a particular scene state in a phase and add more of the building as phases progress.
https://dev.epicgames.com/community/learning/tutorials/Keer/how-to-use-scene-states-twinmotion