What was found
AFTER STARTING THE APU ON APPROACH INTO PHL, THE -SMOKE TOILET- CAUTION MESSAGE ILLUMINATED FOLLOWED BY THE CABIN FILLING WITH SMOKE. THE CREW DECLARED AN EMERGENCY, LANDED AT PHL, DISCHARGED THE APU FIRE EXTINGUISHER, AND EVACUATED THE AIRCRAFT. MAINTENANCE INSPECTED AND RAN THE APU. SMOKE WAS OBSERVED COMING FROM THE ENCLOSURE AFTER SHUTDOWN. THE AIR CONDITIONING PACKS WERE INSPECTED WITH NO DEFECTS FOUND. THE APU AND APU FIRE EXTINGUISHER WERE DEFERRED AND THE AIRCRAFT WAS RELEASED FOR SERVICE. AFTER FURTHER TROUBLESHOOTING MAINTENANCE REMOVED AND REPLACED A CLOGGED APU OIL COOLER ASSEMBLY. THE APU OPERATIONALLY CHECKED GOOD. THE DEFERRALS WERE CLEARED AND THE AIRCRAFT WAS AGAIN RELEASED FOR SERVICE.