A phased tournament is played in sections. You can choose from different starting phases that play at different times and then combine later in the final leg of the event.
Phased tournaments allow you to start a tournament at the time that better suits you.
For example:
Preliminary phases end after a pre-determined number of blind levels have been played, and all remaining players will carry over their chip stack to the next phase.
You're allowed to enter multiple times into the first phases, so if you play Phase 1 and are eliminated, you can enter another Phase 1 and start again. However, if you survive Phase 1, you cannot enter another Phase 1 leading to the same Phase 2. If you survive Phase 1 even with one chip, you'll still get to Phase 2 and won't be able to play another Phase 1.
When you enter a phased tournament, you must ensure that you will be available to play in the future phases as you cannot unregister from Phase 2 (or beyond) in phased tournaments.