Investigators say the girl was waiting on the 400 block of Asbury Avenue Wednesday morning when someone in a black Kia drove up and called her over.
A male suspect threatened her and then grabbed her cell phone, according to investigators.
The student was not injured and was able to call 911.
Police say this same car tried to rob people at two other bus stops in the area on Mountain Avenue and Valley Road.
Police described the vehicle as a black four-door sedan with tinted windows, damage to the front bumper area, and an unknown Delaware registration plate.
Two men and one woman in their late teens to early 20s were inside the car.
If you have any information, call Cheltenham police at 215-885-1600 ext. 400.