A block of ice has little thermal energy. If you place it in a warm room, it melts into warm liquid water, which has much more energy. Where did the energy to turn the ice into water come from?
The energy that is required to change the state of ice into a liquid is obtained in the form of heat energy from the ambient temperature of the warm room.
Once this heat energy is absorbed, the individual molecules of ice gain kinetic energy and start vibrating faster.
Yet, the temperature of the ice remains constant until the ice reaches its melting point because this energy is first utilised to break all the bonds of the lattice structure of the ice.
After all the bonds are broken and all of the ice has changed into water, if more heat is provided again, then the temperature of the water will increase.
