Why boiling is considered a bulk phenomenon?
The temperature at which liquid changes into its gaseous state is called as boiling point.
During boiling of a liquid, say water or milk, heating is to be done from the bottom of the vessel to bring the temperature of the entire liquid to its boiling point - so it is a bulk phenomenon.
But in case of evaporation, the liquid evaporates from the top surface without heating, for example, evaporation of water from the surface of a lake or vesssel. Thus, evaporation is a surface phenomena.