Learn to understand the phasing functionality.
There is only one model. Revit isn't like traditional dumb CAD wherein you just make another plan off to the side or in another file. In Revit, every view is just a set of definitions on how to LOOK at the model. If you make a change in ANY view, you've made a change to that model.
But that change doesn't have to SHOW UP in every view. For example: If you add a wall in a view that is associated with the NEW phase, it isn't going to show up in a view associated to the EXISTING phase.
Best workflow is to set up all these views, and do the modeling in them, prior to annotating.
View: 1st Floor Plan, Existing
Phase: Existing
Phase Filter: New, or All, or Complete
Use: model all the existing conditions here; don't necessarily need this on a sheet.
View: 1st Floor Plan, Demo
Phase: New
Phase Filter: Previous + Demo
Use: demolish existing stuff here; this can be the 'Demo' plan on a sheet
View: 1st Floor Plan, New Work
Phase: New
Phase Filter: Previous + New
Use: model new work here; demo new work here that was only temporary; this can be the 'New' plan on a sheet
View: 1st Floor Plan, Complete
Phase: New
Phase Filter: Complete
Use: just displays the finished condition; you can also model new work here too; you may or may not want this on a sheet
Set the default Plan up as one of those, duplicate it a few times and set each of them up as another one of those, until you have all four.
Possible RCPs include...
View: 1st Floor RCP, Existing (same as Plan, but RCP instead)
View: 1st Floor RCP, Demo (same as Plan, but RCP instead)
View: 1st Floor RCP, New Work (same as Plan, but RCP instead)
View: 1st Floor RCP, Proposed (all same as Plan, but RCP instead)
I humbly suggest you set up four 3D views similarly.
You may also have structural foundation plans...set up four of them similarly and change the discipline.
You may also have mechanical plans...set up four of them similarly and change the discipline.
You may also have electrical power plans...set up four of them similarly and change the discipline.
You may also have electrical lighting plans...set up four of them similarly and change the discipline.
You may also have plumbing plans...set up four of them similarly and change the discipline.
You don't necessarily actually need all four of these types. Once you get used to using phases correctly you will only develop what you need. But having the four types of views will help you gain that understanding. Create the four views, be always conscious of which view you are working in. Work in logical order, modeling the existing stuff first, then demo, then new (and temporary), using the right views.
Option Sets are a whole other ball game, but learn them also.