As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHX - AIR TURN BACK - FLT 0646 - ON CLIMB FROM PHX EN ROUTE FOR ONT THE #2 INERTIAL REFERENCE SYSTEM LIGHT ILLUMINATED, DUE TO WEATHER AT ONT AIRCRAFT TURNED BACK TO PHX. MAINTENANCE REMOVED AND REPLACED THE #2 INERTIAL REFERENCE UNIT, FUNCTIONAL CHECK OF NEW UNIT WAS GOOD.