What happens to the heat that is being added to the beaker during the phase change?

The heat supplied during the phase change leads to the change in molecular structures, crystal structures of the substance.

Explanation:

During a phase change, either melting or boiling, the temperature of the substance remains fixed. This is because, if the substance was a solid, then it needs energy for destruction of the crystal structure and gain the particular molecular conformation to be a liquid. Similarly in case of a liquid boiling, it needs energy to overcome the molecular cohesive and adhesive forces to leave the liquid state and become a gas.

So when even after supplying heat the temperature of a system doesn't rise, that means the system is performing equal amount of work. That's why the temperature doesn't increase. This is mentioned as the latent heats in physics.

The heat is used for breaking the bonds of the molecules in the beaker.

Explanation:

In the beaker liquid phase is there suppose it is water the heat provided will be used up in breaking the bond and overcoming the forces that keep the molecules together.

The temperature does not change during phase change.

The heat energy provided will cause the molecules to be far apart.

The added heat will be stored as potential energy.