In physics, this term means the disconnected transition of a system from one phase to another. Passage of ice into water, water into steam … In doing so, latent heat is consumed (or emitted, depending on the direction of change). It looks like nothing is happening, the temperature doesn't change until the system passes into a significantly different state.
Here, phase transition is meant at the level of the logic of social organization. The system represents society, and the phase represents dominant logic; a set of dominant principles that shape social processes. Like processes of production, valuation, shaping of worldview, mastery of nature and others. Phase transitions thus represent the transition of a society from one dominant logic, from one set of dominant principles, into a new logic.