Gel phase occurs after you've poured your soap into the molds (when doing cold process soap).  The soap will become super hot (reaching tempreatures up to a full 190ºF) and get a translucent, jelly-like look to it.  This is a normal part of the soapmaking process. 

However, gel phase is not necessary to make your cold process soap turn out.  If your soap doesn't go through gel phase, don't despair.  While the look and feel of non-gel phased soap is slightly different than soap that has gone through the gel phase, it is mostly a personal preference thing.  Either type of soap looks and feels great once it is fully cured.  Below are a few examples of the typical appearance of a gel phase: