Police said the attack happened at the Western station just before 4 p.m.
A 31-year-old man was standing on the platform when a suspect, identified only as female, forcefully took his phone.
When the man tried to get his phone back, another suspect, identified only as male, attacked him multiple times with a hammer.
The victim suffered multiple lacerations to his head and was transported to Stroger Hospital in good condition.
No one is in custody and Area Four detectives are investigating.
Police did not immediately provide further information.
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