Answer:
Melting.
Step-by-step explanation:
Phase change is when a state of a matter changes to another.
For example
a) conversion of solid to liquid : It is a phase change known as melting.
b) conversion of liquid to solid: it is a phase change known as freezing.
c) conversion of solid to gas : It is a phase change known as sublimation.
d) conversion of gas to solid: it is a phase change known as solidification.
e) conversion of liquid to gas : It is a phase change known as vaporization.
f) conversion of gas to liquid: it is a phase change known as liquefaction.
The other options are not phase change
crushing: it simply conversion of a large particles of solid to smaller
expanding: it is again conversion of a gas to higher volume gas
burning: it is a chemical change where a substance undergoes burning.