Phantasm has always been one of those horror films that is on every list and is supposed to be so good, but is in fact incredibly disappointing and ineffective as both a horror film and an adventure film for me. I decided to rewatch it and the entire series to see if I could find that element everyone else is getting but me.
I still find the first film to be an incredibly poor attempt at horror. I read into the same metaphor as I did initially: the child is discovering his sexuality and is conflicted because he feels that his self that he knows must die if he grows up and into his sexuality, featuring the tall man as the erection that keeps popping up, the destructive balls that drop and seek to bore through any and everything, seeking out flesh and splooging life juices out once the penetrate said flesh. In later films we learn that when peopel die they turn into shrunken, withered flesh creatures who are controlled by the tall man and have had their brains placed inside the balls. Having never seen the first film as a child, the sense of adventure is not as grand as it could have been for me.
The sequels, however, transform the series into a much more interesting adventure with a Tall Man mythos unfolding as you travel with the self appointed hunters and become part of their team, learning the ins and outs of the universe along with them. Though they are a bit campy in places, they are still very fun, and each sequel picks up where the last film left off making for a relatively seamless experience if you are marathoning them (some of the actors change, but it is hidden fairly well). The loss of innocence as related to the discovery of the tall man, the balls, and the shrunken flesh zombies seems to carry throughout the series. So if you are like me and found the first film lacking, you should try the rest of the next film to see if the tonal shift makes the series work for you.