it asks for a one sentence

Question

rule about relationship between phase changes and temperature

and

rule about phase change and heat energy

Answer 1

The rule about the relationship between phase changes and temperature:
"The temperature remains constant during a phase change."

The rule about the relationship between phase changes and heat energy:
"Heat energy is absorbed or emitted during a phase change." (For water, for example, heat energy is absorbed when changing from a liquid to a gas and heat energy is emitted when changing from a gas to a liquid.)