What is thomas the phantom horsewoman about?

There's no widely known story or legend called "Thomas the Phantom Horsewoman." It's possible you're thinking of a different name or a story that's more obscure.

To help you, could you provide any more context? Perhaps you remember:

* Where you heard about it: Was it a book, movie, TV show, or a story you heard from someone?

* Any details about the story: What is the main character like? What is the story about?

* Any other names or words associated with it: Do you remember anything else that might help identify the story?

With more information, I can try to figure out what you're thinking of.