A319 PARKED AND CHOCKED IN PHL MOVES AFTER PARKING BRAKE IS RELEASED. CHOCKS WERE PLACED ON THE PAINTED LINE WHICH CREATED LITTLE FRICTION ON A WET SLICK RAMP.

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ARRIVED AT GATE. ACFT STOPPED AND PARKING BRAKE SET. CHOCKS-IN SIGNAL RECEIVED FROM GND PERSONNEL AND I ACKNOWLEDGED THE SIGNAL. APU OFF. JETWAY BROUGHT UP TO ACFT AND ELECTRICAL PWR CONNECTED. #1 ENG SHUT DOWN. AFTER ENG SPOOLED DOWN; THE PARKING BRAKE WAS RELEASED. AFTER ABOUT 5 SECONDS; NOTICED THE JETWAY PASSING THE COCKPIT SIDE WINDOW. AT ABOUT THIS TIME THE 'A' FLT ATTENDANT STATED 'THE JETWAY IS MOVING.' THE COCKPIT AND CABIN DOOR WERE BOTH OPEN; BUT NO PAX HAD DEPLANED. APPLIED THE TOE BRAKES AND STOPPED THE ACFT AND RESET THE PARKING BRAKE. WENT ONTO THE JETWAY AND DOWN THE OUTSIDE STAIRS. THE NOSEWHEEL WAS CHOCKED; BUT IT HAD PUSHED THE REAR CHOCK AFT ABOUT 4 FT. THE MAIN GEAR WAS NOT CHOCKED AND THE TUG AND TOW BAR WERE NOT CONNECTED. INSPECTED THE PAINTED LINE WHERE THE CHOCK HAD SLID AFT. DUE TO DRIZZLE; THE RAMP WAS WET AND IN THE PAINTED AREA WHERE THE CHOCK WAS PLACED WAS EXTREMELY SLICK. SLIGHT DAMAGE OCCURRED TO ACFT WHERE THE BELT LOADER HAD BEEN POSITIONED. ABOUT A 1 INCH LATERAL HOLE IN THE ACFT COMPOSITE BELLY PANEL WAS CAUSED BY THE IMPACT WITH THE BELT LOADER. THE TOTAL TIME FROM WHEN THE PARKING BRAKE WAS SET AT THE GATE AND WHEN THE ENG WAS SPOOLED DOWN AND THE PARKING BRAKE RELEASED WAS ABOUT 2 MINS. I BELIEVE THE CHOCKS-IN SIGNAL SHOULD NOT BE GIVEN UNTIL THE NOSE GEAR AND MAIN GEAR ARE CHOCKED OR THE NOSE GEAR IS CHOCKED AND TOW BAR AND TUG CONNECTED. ALSO ON THE TXWY FACING GATES IN PHL; EITHER THE GATE MESSAGE OR THE ARPT ADVISORY PAGES SHOULD HAVE A STATEMENT CONCERNING LEAVING THE PARKING BRAKE SET IN WET OR ICY CONDITIONS.