What is phase congruency?
The more that sinewaves that have a zero crossing in the same direction at the same point add up in magnitude, the greater the contrast at that point.  e.g. a possible edge.  Phase congruency is another name (actually a superset) for the amount of sinewaves that line up with zero crossings at (nearly) the same point or points.

Whereas a random distribution of phases is more likely to result in something that a human would see as uniform noise rather than an edge.