Not so fast!
I don’t know about the phosphine, but of course they found ammonia. It’d be remarkable if they didn’t.
How you figure? Ammonia is composed of nitrogen and hydrogen. Venus has nitrogen (roughly the same amount as Earth), but the one element Venus is really deficient in is hydrogen.
You can’t avoid all hydrogen. When high-energy protons (i.e., hydrogen ions) from the solar wind hit Venus, it’s natural that they’d turn some of the nitrogen into ammonia.