Seven teenagers were arrested Tuesday night after they ­allegedly assaulted a 34-year-old Boston woman on an ­Orange Line train, stole her cellphone, and then celebrated with high-fives as they ran out of the MBTA station, the Suffolk district attorney’s office said.

Transit Police officers met the woman at the Tufts Medical Center T Station, after she had allegedly been grabbed by the hair and had her face slammed into the train’s metal railing as the teens pried her phone from her hand, District Attorney Daniel F. Conley’s office said.