What happens to the temperature of the substance during a PHASE CHANGE?

Write down only INCREASE, DECREASE or REMAIN THE SAME.
GIVE A REASON for your answer.

ice stays at 0 C during transition to water or back to ice.

Same deal at 100 C between water and steam.
If you pump heat into the pan to boil the water, it gets used to make steam during the whole process once boil starts and if a water drop hit101 it would transition to steam.