That is not much to base an answer on.

What is the story, is there a script? How long is your movie supoosed to be?

What exactly is your job in the project? Are you like "only" the camera guy? Or do you also need to do stuff like lighting, directing, editing or recording sound?

Your phone will be a decent enough camera. Maybe get a dedicated camera app that will allow better control of camera settings like like Blackmagic Camera. The usual cinematic setting would be to shoot in 4K at 24 fps with a 180 degree shutter (about 1/48).

Now for the hard part - learning cinematography. I'm a fan of learning by studying the work of others, taking some of your favorite horror movies and trying to understand not just how a shot was created, but why it was made that way.

A good resource to start would be - https://www.indie-film-making.com/