Phase changes can be brought about by heating or cooling. For example if water (a liquid) is heated enough, it evaporates and becomes water vapor or steam (a gas). This kind of phase change--liquid to gas--is called evaporation or vaporization. Water vapor can in turn be cooled to form liquid water.
I don't know what your question is but if you're wondering what is called when water changes from a gas to a liquid phase the answer would be Condensation
