A man sexually assaulted a 15-year-old girl whom he allegedly grabbed and took into an alley as she headed from a Bronx elevated-train station, cops said.

Javon Grant, 22, was hit with sex and robbery raps in the attack on Amethyst Street Tuesday at 9 p.m.

The girl was returning from walking her friend to the station. Grant also allegedly took her iPhone and was nabbed with the help of surveillance video, cops said.