The kinetic energy (energy of motion) of the particles that make up a substance determines the state of the material. During phase changes, energy increases, but the temperature does not increase, until all of the material has changed phase. Energy and stresses cause changes in physical properties of all materials--solids, liquids, and gases.
Demoin, Dustin, "Gases, Liquids, and Solids [9th-12th grade]" (2009). Understanding by Design: Complete Collection. 95.