Phantoms, the movie, is the screen adaption of a Dean Koontz novel. While I consider Koontz to be a good writer, I don't think he's great (sticking to the style of supernatural horror written by Koontz, I think only Stephen King and Peter Straub, to a limited degree, are great in this category). And unfortunately his "good" stories turn end up being mediocre or worse on the movie screen (take, for example, Hideaway). As a fan of horror novels and movies, I'm generally used to the idea that the book is much better than the movie. But in my opinion, Phantoms is the case of an "okay" book being turned into a mediocre movie.
In Phantoms, two sisters (Joanna Going and Rose McGowan), along with a sheriff (Ben Affleck), and a tabloid news reporter, Timothy Flyte (Peter O' Toole), end up battling an evil from Earth's ancient past in Snowfield, Colorado. This creature, which has existed for millenia, has slowly become sentient as it consumed more and more creatures and somehow acquired their memories, knowledge, and among other things, an ego. Thinking it is the devil, the creature stages an elaborate snare to draw Flyte to Snowfield, so he can "spread its gospel" in his tabloid.
The book is indeed somewhat better, mainly because there is more character given to the "the Ancient Enemy." Phantoms, the movie, has its scary moments but they grow tiresome by the end. However, at the beginning, while the girls are still investigating the cause of an entire town's extinction, the movie is quite terrifying. Worth the matinee fare on the big screen, even if it is just to see O'Toole trying to hold back from grinning.