The robbery occurred April 20 near the intersection of Foster St. and Sheridan Road. The victim, a 24-year-old Northwestern University graduate student, was walking while talking on his phone when someone grabbed the phone, a Samsung Galaxy 3, from him and ran.
The victim initially attempted to chase down the robber, who then yelled he would shoot the victim.
Police tracked the phone to a cell phone store on the North Side, recovered the phone and got the name of the person who sold the phone to the store.
Police say the victim identified the suspect in a photo lineup. They then arrested Mitchell J. Ratliff, 22, of Chicago's North Side, on Sunday.
Police say Ratliff admitted to the crime and charged with robbery and theft.