Was Joey socialized with larger dogs when he was a puppy?

Considering what happened with your cat, I can certainly understand why you yourself are so fearful, but do not convey these emotions to Joey and I would highly discourage seclusion. Secluding him from large dogs will not help him nor you. The only way to curb his fear is to confront it (positively, of course).

Don't feel bad! I've worked with several people with fear aggressive small dogs. For some reason, fear aggression seems more pervasive in the world of small dogs. However, there is plenty of help available. Knowing this about Joey, I would also recommend finding a behaviorist to help you with both basic obedience and his fear.

(P.S. Clickers are WONDERFUL with fearful dogs. I used 100% positive reinforcement w/ clickers on the aforementioned dogs, and the results were always very solid.)