What is the energy that is absorbed or released during a phase change?
If that is a first order phase transition, i.e. the first derivatives of the molar Gibbs function undergoes discontinuous changes during phase transitions, then there is some heat involved in the phase transition (heat released/heat absorbed).
That heat energy is known as the latent heat and equals to the change in enthalpy during the phase transition.
An example of phase transition involving latent heat is-
Ice <-> Water <-> Steam
However, there are other phase transitions known as second order phase transitions where there is no latent heat involved. (Ex - Ferromagnetic to Paramagnetic phase of a solid at Curie Point).