It will be at least a year behind bars for the Philadelphia woman who struck and killed a teenage girl on Germantown Pike near Plymouth Whitemarsh High School 13 months ago.   20-year-old Stephanie Phillips left the scene of the accident without stopping.   She was also driving with a suspended license.    The victim ran out into the highway during a rainstorm while students were celebrating the P-W High School state basketball championship.   Montgomery County law enforcement officials say Phillips would not have been charged if she would have stopped immediately after hitting the teenager.