I've encountered flibbertigibbet and Brobdingnagian. Never encountered hippopotomonstrosesquippedaliophobia before, at least I don't remember encountering it.

Flibbertigibbet appears in some of the Little House on the Prairie (Laura and Mary) books, if I remember right.

And I've also read Gulliver's Travels which is where Brobdingnagian comes from. Brobdingnag was a land of giants. Pretty sure I've seen the word used elsewhere though.