Robert Hicks, 52, was at the hospital on Midland Avenue when he began to cause a disturbance at the hospital when he attempted to use the phone without permission, police said.
When hospital security tried to calm Hicks down, he became violent and began to strike the guard numerous times with the phone, police said.
The security guard was injured and received treatment at the hospital.
Hicks was charged with two counts of assault, felony criminal possession of a weapon and misdemeanor criminal possession of a weapon, police said.
He is being held at the Rockland County Jail and is scheduled to appear in court on Thursday, Feb. 23.
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