Could the entity who made them be the ones chasing the vasari empire?
Probably. I think in other places it says the Vasari are the only ones that can make the phase jump inhibitors, but they can only do it by using nanobots to replicate them, they really have no idea how they work. The Advent and TEC have both gotten theirs by stealing them from the Vasari.
My personal bet is that whatever is chasing the Vasari are some sort of demons or are some ancient race like the Antarians from Master of Orion II that were trapped in a different dimension long before the Sins races evolved. Some Vasari phase experiment likely let them out of their prison, allowing them to come back to this dimension.