Why does water change phase so easily?
does water's polarity help explain its unusual phase properties?


Not just its polarity, but its ability to form hydrogen bonds, together with the size and shape of its molecules. 

Hydrogen bonds give water an unusually high boiling point for a molecule its size; many molecules of similar size that can't hydrogen-bond are gases at room temperature. They also give water a relatively high heat capacity and high enthalpies of fusion and vaporization. These latter two properties mean that ice has to absorb more heat to melt and liquid water has to absorb more heat to boil than would otherwise be necessary without hydrogen bonding.  

Water's shape lets it form 4 tetrahedrally arranged hydrogen bonds. This lets it hydrogen-bond into networks of chair-shaped hexagonal rings in ice. The voids in the center of the rings make ice less dense than water. This is unusual; the solid form of a compound is most often denser than the liquid form.