It might be reaching to call this a phobia or an imperfection, but he's easily embarrassed by certain things, like the sunbathing in LOVELY BUT LETHAL or the model in SUITABLE FOR FRAMING.
There's also the first Cathy Goodland and Ken Nichols scene in GREENHOUSE JUNGLE. He doesn't SAY anything, but Cathy picks up on it right away. (Most people would agree with his reaction to it, though I can't help liking Cathy's "I don't care what anyone thinks" attitude.)
The scene in "Murder, a Self Portrait", when they find Louise dead on the beach, the other two ladies, Vanessa and Julie run up to Max Barsini and comfort him. I could tell that Columbo was easily embarrassed by their reaction and the way they showed the attention to Max.
This is another very understandable one, so you'd hardly even call it a phobia.
In spite of all the murder victims he's seen, there are some kinds of wound that still get to him. Oddly enough, that includes a wound on a LIVE person, Paul Galesko.