They've hit a dozen Metro PCS stores across the city in the past month.
Surveillance video shows the men, wearing hoodies and bandanas, entering the store in the 3100 block of Kensington armed with guns and a machete.
"They would order the employees to the ground, they would put the guns to their heads, they would put a knife to their heads, they would demand access to the safe," said Chief Inspector William Colarulo of the Philadelphia Police.
Action News spoke to one of the workers who was there that night.
"I quickly tried to hide," said Pamela Ortiz. "Then, one of them came up to me and put a gun to my face, telling me to stay down."
Ortiz said, before long, the men had cleaned out the register, the safe, and they even took her pocketbook and iPod.
"It all happened so fast. In less than three minutes, it was over," Ortiz said.
12 Metro PCS stores have been hit by the bandits since November 29th. In once instance, they got away with $5,000 in cash.
"It's a miracle there have been no injuries as a result of these robberies," Colarulo said.
Metro PCS sells cell phones to people with no credit, meaning they deal in a lot of cash. In one heist, the thieves got away with more than $5,000.
Monday night, security teams were brought in to change the way they do business.
"We've definitely tightened our security measures," said marketing director Jeremy Johnson. "As you can see on the wall, we have cameras up there."
Other changes: No more than $50 will be kept in the registers at any time, employees will not have access to the safe, and workers will be able to control who gets inside the store.
"The stores will have buzzers, we have to buzz you in. If you look suspicious, we won't buzz you in," Johnson said.
On Saturday investigators got a break, after alert 25th District officers noticed something amiss at the store on East Airy Avenue. They interrupted a robbery in progress and arrested five people.
Police think there may be others out there who are involved.
"We certainly are not ruling out there may be other people who were involved with these robberies throughout the tristate area," said Colarulo.
If you can identify the people involved the people involved in these robberies, you're asked to call police at 215-686-3396 or 215-686-3397.