Phthalo blue is short for phthalocyanine blue. The pigment is made when phthalocyanine binds with copper. Phthalocyanine is synthesized using various derivatives of phthalic acid. Phthalic acid was obtained by Auguste Laurent, who thought he had created a naphthaline derivative, which he named naphthalenic acid. When another chemist showed that it was not a naphthaline derivative, the name was changed to phthalic acid. Naphthaline was derived from naphtha. The word naphtha comes from Latin and Greek... in Ancient Greek it refers to any sort of petroleum or pitch.So now you know where the word phthalo comes from too. :) (To learn more of the fascinating details on each of these compounds, search for them at Wikipedia.)
PS: Mr Party-Of-One is currently playing rap music with rude lyrics. Thankfully I can't hear much more than a muffled thumping up here, but the lyrics can be heard clearly in the hall.