The phase gates were created by the Adronikos Empire in order to connect their galaxy spanning Empire. This was a major improvement over the Otamic Empire relying on the limited use of FTL to connect their various planets. The phase gates seem to be made out of an extremely strong alloy that has been unable to be replicated by the Alliance. This alloy can survive super novas, and other natural occurrences in the space.
The phase gates use dark energy to create a direct link to another phase gate. The two phase gates create an Einstein-Rosen Bridge or wormhole between the two allowing instant travel between the two. In order for this link to happen ships have to send the message how much mass they are carrying and the gate will compensate to widen the bridge and spend more power maintaining the bridge.
The phase gates have the ability to transport whole space armadas through another gate instantly.