I'm guessing it applies human cognition to the task of understanding what people want when they say "fantasy landscape" using human heuristics and pre-alters your prompt to get you a closer result to your imagination than that simple keyword.
Phantasmagoria is a consumer product, geared towards people who don't want to know anything about what a prompt or a sampler is. It's the difference between Dropbox and using SVN or CVS on a curlftpfs-mounted FTP account.
Or even better running stable diffusion locally?