Energy is needed for the phase of matter to change.
But, during the phase change, the substance requires an extra amount of heat to melt. This is known as latent heat of fusion. In the same way, when a substance vaporizes, it needs an extra amount of heat energy. This is known as latent heat of vaporization.
The temperature remains constant because all of the heat energy supplied is used for the change of phase of matter. Temperature of liquid does not change during evaporation because the heat taken by the water from the surrounding is used to convert the state of water from liquid to gas by increasing kinetic energy among the molecules and this kinetic energy increases the intermolecular space. Thus changing the state of water. Therefore there is no rise in the temperature of the water.