The strong arm robbery occurred around 4:20 a.m. inside the Jackson Blue Line subway at 328 South Dearborn Street, said police.
Investigators said a male offender attacked a male passenger and grabbed the commuter's iPhone from his hand.
The robber was described as a black male with a medium complexion, about 35-years-old, 6’2”, and 220 pounds.
The thief was wearing a light red t-shirt and shorts.
The iPhone thief was last seen running southbound through the Jackson Blue Line tunnel, said police.
After receiving a police escort to his intended destination, the victim decided to file a police report at a "later date".