And yes, it's free. There are optional microtransactions for the multiplayer mode, but nothing free-to-play interferes with the single-player mode.
If yr having trouble finding Phantom Dust on the web Microsoft store, here's the link: https://www.microsoft.com/en-us/store/p/phantom-dust/9pcdnbhr11mr
For those who aren't familiar: Phantom Dust was the next game by Yukio Futatsugi, formerly of Sega, after directing Panzer Dragoon Saga. It's a post-apocalyptic third-person action game with CCG elements - and it really works very well.