To begin setting up phases, you will find Phasing under the Settings pulldown menu. The dialog box is divided up into tabs. The first tab is where you set up the names of your phases. You will notice that the dialog box has Past on the top and Future on the bottom. It is important to order your phases chronologically. The default template comes with two default phases-- Existing and New Construction. You can rename the defaults or add new phases by clicking on the Before or After buttons in the Insert section.
Most people, including myself, think that Demolition is a phase in a project. With Revit, it is a Phase Status. Let me explain. You could have demolition in any or all phases of your project. It is just part of that particular phase. There are 4 default phase status' that can be used on every phase. You can set items to either Demolished, Existing, New, or Temporary in each phase. The following chart defines each of the phase states.
I hope this helps expand on what Steve wrote about. Phasing in Revit works well if you understand the concept of phases, phase states, and how to apply them to views.