“Optimist” is a word which here refers to a person, such as Phil, who thinks hopeful and pleasant thoughts about nearly everything. For instance, if an optimist had his left arm chewed off by an alligator, he might say, in a pleasant and hopeful voice, “Well, this isn’t too bad. I don’t have my left arm anymore, but at least nobody will ever ask me whether I am right-handed or left-handed,” but most of us would say something more along the lines of “Aaaaah! My arm! My arm!”