While it's certainly a long and impressive word, it's only 36 letters long.
There are actually several words that are longer, including:
* Pneumonoultramicroscopicsilicovolcanoconiosis (45 letters) - a lung disease caused by inhaling very fine silica dust.
* Floccinaucinihilipilification (29 letters) - the act of estimating something as worthless.
And, of course, you can always create longer words by combining existing words or adding prefixes and suffixes!
So, while "hippopotomonstrosesquippedaliophobia" is a fun word to say and remember, it doesn't quite hold the title of the longest in English.