The incident happened at 5:22 p.m. Friday inside the Godfrey Food Market located at 912 Godfrey Avenue in the city's Summerdale section.
Police say when the victim left the market walking towards 10th Street, she was followed by a male suspect.
The suspect, police say, ran up from behind, pushed her on her face, then grabbed her cellphone from her hands.
The suspect fled and was last seen north on 10th Street then west onto Godfrey Avenue.
Police say the suspect was with two other unknown males as he entered the market.
The victim did not sustain any injuries during the incident.
The suspect is described as black male, late teens to early 20s, thin build, thin beard and mustache, short black hair, light complexion, wearing a white thermal shirt, and light colored pants.
Anyone with information should contact 215-686-TIPS (8477) or text a tip to PPD TIP or 773847.