What do you mean by bulk phenomenon?
Why boiling is called bulk phenomenon?
The process which involves total molecules including interior molecules along with surface molecules is called a bulk phenomenon.
Example: Boiling of any liquid.
Boiling is a bulk phenomenon. Particles of the liquid gain enough energy to change to a vapour state. The entire liquid and all the molecules including the interior and the surface gain energy to change to a vapour state.
The heat energy is supplied from the bottom of the liquid. Therefore the heat energy goes to the entire bulk of the liquid and starts boiling.
Whereas evaporation is a surface phenomenon. Only the particles on the surface gain enough energy to get converted into vapour state. A small fraction of particles at the surface gain energy and break away from the force of attraction of the other particles and changes to vapour state.