Hippopotomonstrosesquippedaliophobia is rather long, however, I don't know if it's the longest one. Ironically, it is the fear of long words.
There isn't a phobia that specifically covers letters, but "Logophobia" is the "Fear of words.".
phobia
Pneumonoultramicroscopicsilicovolcanoconiosis is 45 letters long... and The phobia is 36 letters long, so the lung disease is longer.
Ranidaphobia is fear of frogs (12 letters).Batrachophobia is another word (14 letters).Frog phobia is also used (10 letters, but two words).
Tachophobia is the term that most phobia lists use to refer to the fear of speed.
Cluastraphobia. Most people who have this phobia really don't like enclosed, tight, spaces.
Measuring at a mere 34 letters long, it's the definition of a phobia of long words. So if you're having trouble looking, reading, or even thinking about hippotomonstrosesquippedaliophobia, then you may be suffering from this phobia.
a phobia is not as much a phobia as much as it is more of a mental disorder
From what I understand there is no specific phobia for people who are afraid of mail. Most just call it Mail Phobia...
Arachnophobia is the fear of spiders. It is the most common phobia and the statistics show that 50% of women show signs of having some form of the phobia.
Venustraphobia - Fear of beautiful women.
It is said that he had a phobia about cats.