Friday 13th

The phobia of Friday 13th is called (according to Wikipedia)

Friggatriskaidekaphobia (Frigga is the name of the Norse goddess for whom Friday is named and triskaidekaphobia means fear of the number thirteen)

or

Paraskevidekatriaphobia (the Greek words Paraskeví meaning Friday and dekatreís meaning thirteen)

I don't know what the phobia of having to spell either of these words is called, but I bet it's impressive.