Now I know you shouldn't laugh at phobias. Yet when I looked at the definition for this one, I couldn't help it... (Sorry!!)
I don't know the answer to the question. Presumably seeing a duck (or indeed a platypus) does not make a difference to people who are anatidaephobic, seeing as they always think that they are being watched by a duck, whether or not there's actually one around.
It must be an interesting and challenging phobia to have.