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.