Good question. After reading your post, I went to Amazon and looked up the book The Vampyre by Polidori. I used the “Look Inside” feature to peruse and on page 11 of the book I found a reference to a “German work” titled Phantasmagoriana.
According to these articles:
http://www1.phillyburbs.com/dracula/introduction.shtml
http://www.petercushingmuseum.com/genderfrank.htm
Phantasmagoriana, inspired Lord Byron, Mary Shelley, and Polidori to write their own horror tales. Shelley created Frankenstein and Polidori created The Vampyre. So is the signficance in the reference/name? The fact that a German horror tale title Phantasmagoriana was the inspiration for 2 of the most recognizable stories in all of horror history?
I would love to be able to find a translated copy of Phantasmagoriana somewhere. I cannot find anything using Google though.