American International Pictures specialized in crap, but even for AIP, this is a bad one. The Phantom from 10,000 Leagues is among the most tedious, least interesting films I’ve ever seen. It’s a monster flick that has more dialogue than a Merchant Ivory costume drama, and all of it is inane. There’s even a spy angle that does little more than stretch out the running time and subject us to more talking. And the monster? It’s a rubber suit, but it could just as well have been a statue for all the trouble Norma Hanson, who was in the suit, had moving around. Phantom is a direct challenge to a viewer’s attention span. If there is a smartphone within reach, I defy any viewer to watch this flick without picking it up.
Directed by Dan Milner from a screenplay by Lou Rusoff, Phantom tells the story of science gone wrong. A monster that sort of looks like a Chinese dragon is terrorizing local waters. Professor King (Michael Whalen), a marine biologist, has been creating mutant lifeforms with atomic radiation, and it’s one of his own experiments that is out in the world causing trouble.
Another scientist, Dr. Ted Stevens (Kent Taylor), and a federal agent, George Thomas (Phillip Pine), are on the case after bodies, victims of the monster, begin washing up on shore. 
Meanwhile, yet another scientist, Bill Grant (Rodney Bell) is trying to steal King’s work and give it to a foreign spy (Helene Stanton) to get out of a honey pot trap.
That’s a lot of plot for a monster flick, and it doesn’t leave a lot of room for the actual monster. The monster shows up to remind viewers they’re still watching a monster flick, but it’s peripheral to the stuff that happens on land. But, more monster and less talking wouldn’t have done much to help. The monster suit has little of the artistry that was shown in Creature from the Black Lagoon, for example. and the underwater photography is muddy. In addition, all of the monster scenes look like they were shot as one or two sequences and then distributed throughout the film as needed. It’s supreme cheapness.
The strongest impression one gets from this film is length, and yet the running time is a mere 80 minutes. But, time is relative. 80 minutes would make for a swift Star Wars flick (Disney take note, please), but when it comes to a slog like The Phantom from 10,000 Leagues, minutes are like hours. This is an unwatchable mess of a shitty movie, sending it way down the Index, landing with a dull thud at #232, between Mazes and Monsters and The Human Centipede. Stay away.