The incident took place Tuesday at 7:35 p.m. at the MetroPCS store on the 4200 block of North Broad Street.
Surveillance video of the robbery was released Thursday.
Police say two men wearing masks entered the store.
One suspect went behind the counter and pointed a black handgun at the clerk. He demanded the clerk get on the floor as the second suspect detained a customer.
The first suspect then grabbed the clerk by his neck and threw him to the floor and started taking the money.
The clerk then got up and grabbed the suspect's arm to stop him.
The suspect then struck the clerk in his head with the gun.
Seeing that the gun was plastic, police say the clerk got up again and attempted to stop the suspects.
The suspect fled with approximately $1,000.
The first suspect is described as a black male, 20 to 25 years old, 6', 160 pounds, wearing a dark mask, white t-shirt, blue jeans and dark sneakers.
The second suspect is described as a black male, 20 to 25 years old, 6, 160 pounds, wearing a dark mask, white long sleeve shirt, blue jeans and white sneakers.
They fled in an older model dark colored sedan, possibly a Nissan Maxima and a beige or gold colored small SUV.
If you see these suspects do not approach them, contact 911 immediately.
To submit a tip via telephone, dial 215-686-TIPS (8477) or text a tip to PPD TIP or 773847.