Tetraphobia. It does exist.

The Korean, Chinese and Japanese words for the number four are the same as the word for death. It is their unlucky number in the same way 13 is for us, except it be like saying eleven, twelve, death, fourteen when counting from my understanding. 

Often times in elevators the simply have a capital F instead of the number 4. I assume it stands for "four", which is pretty funny since the Korean word for four is "sa". Seems like it should be an S instead. 

I discovered from Wikipedia (obviously, completely reliable source) that this fear is known as tetraphobia. You'd better make sure you don't have it...