Nicole L. answered  04/30/20
Experienced chemistry teacher
Boiling is the change of phase from liquid to gas.
Sublimation is the change of phase from solid to gas.
Efflorescence is, according to dictionary.com
- to change either throughout or on the surface to a mealy or powdery substance upon exposure to air, as a crystalline substance through loss of water of crystallization.
 - to become incrusted or covered with crystals of salt or the like through evaporation or chemical change.
 
Based on these definitions, each word describes a process where the final product results in a gas (probably water) through a phase change. In the case of boiling and efflorescence, evaporation occurs. In the case of sublimation, a larger phase change shift happens, but some part of it still ends up in the gas phase.