Phyllactinia alangii is a species of powdery mildew in the family Erysiphaceae. It is found in Asia, where it affects the genus Alangium.
The fungus forms white, thin growth on the undersides of host leaves. P. alangii, like most Erysiphaceae, is highly host-specific and infects only the genus Alangium. Other species of powdery mildew (in the genus Erysiphe) have also been reported from this host genus.
The fungus was formally described in 1979 by Y.N. Yu and Y.Q. Lai.