Phoenix Police say it happened Monday at a Motel 6 near I-17 and Indian school Road.
According to police, they got a call from the girl's mother asking them to investigate claims that the child was alone in the room.
The girl was supposed to be in the custody of her father, Timothy Bell.
Police found the hotel room door open and the infant alone and on the floor.
Bell was arrested when he returned to the hotel from work. He's been charged with one count of child abuse, and possession of a weapon by a prohibited person.