Triskaidekaphobia is from Greek treiskaideka, triskaideka, thirteen
(treis, three + kai, and + deka, ten) + phobos, fear.
In Christian countries the number 13 was considered unlucky because
there were 13 persons at the Last Supper of Christ. Fridays are also
unlucky, because the Crucifixion was on a Friday. Hence a Friday
falling on the thirteenth day is regarded as especially unlucky.
Some famous triskaidekaphobes1:
Napoleon
Herbert Hoover
Mark Twain
Richard Wagner
Franklin Roosevelt
However apparently the Chinese considered it lucky.
Gee now we can use the proper name for the phobia. However there are
web sites with therapists advertising complete quick cures for the
phobia. An from what I have read phobias are fairly easy to treat.