Get Phased

Phases in Revit aren't hard, but they can be a bit confusing. At first glance, they seem easy - Existing and New Construction. The key is understanding that each phase is a moment in time. With just two phases, it's not that big of a deal, but if you were to add more phases, this concept becomes more important. If an element is existing, you set it as Phase Created = Existing, if it's new, you set it as Phase Created = New Construction (Element Properties-Phasing-Phase created). If you're going to demolish something existing, set it as Phase Created = Existing, Phase Demolished = New Construction.

All this is simple enough, but elements won't display differently in views until you set up phase filters and graphic overrides. The Phase Filters require setting up display styles for New, Existing, Demolished, and Temporary. This is where things could get a little confusing. The "Existing" in Phase Filters isn't necessarily the same as the Existing in Project Phases. This is where thinking of the Project Phases as moments in time can be helpful. Therefore, Phase Filter "Existing" is anything that was created before the phase that each particular view is set to (View Properties-Phases). Setting the view to a phase is the equivalent of taking a snapshot of that moment in time. If your view is set to Phase Existing, unless you've created another phase (moment in time) before Existing, the Phase Filter "Existing" will be empty, because there is nothing that could have existed prior to Existing. (Confused yet?) Any element that was created in the current View Phase (Existing) and not demolished in the current View Phase would be read as Phase Filter "New" in this view. Phase Filter "Demolished" applies to elements created prior to the current view phase and demolished in the current view phase. Phase Filter "Temporary" applies to elements created and demolished in the same (and current) view phase.

Ultimately, successfully using phases requires some advance plannning and care. Spending 10 minutes at the onset of a job to plan out the phases and understand what each phase and phase filter should show will result in better experience.

For a more in depth look at phases (and a way better explanation than I could give) look here. (MEP check this out as well.) Interesting thoughts on showing future work here.