What does the root "phyllum" mean used botanical binomial nomenclature
Binomial names often use of greek words. Phyllum means -- as you correctly stated -- "leaf", but is not derived from latin but from the greek φύλλον, 'phyllon'.

By the way, there are also lots of examples where the latin word 'folium' is used. To stick with the genus Acer from your example, there is another species named Acer gracilifolium. So don't be confused by the linguistic chaos in binomial nomenclature.