What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND THE AIRCRAFT DIVERTED TO PHX DUE TO THE FLIGHT CREW REPORTING THAT DURING CRUISE FIRST OFFICERS OXYGEN BOTTLE ECAM INDICATION DROPPED BELOW MINIMUM FLIGHT CREW REPORTED THAT IT INDICATED 490 AND KEPT DROPPING. THE AIRCRAFT LANDED SAFELY AT PHX WITH OUT FURTHER INCIDENT. THE FLIGHT CREW REPORTS THAT ON LANDING IN PHX THE INDICATION WAS 430. MAINTENANCE FOUND THE 3RD OBSERVER STORAGE BOX UNION TO BE STRIPPED / LEAKING AND REPLACED THE BOX PER AMM 35-12-41. A SATISFACTORY LEAK / OPERATIONAL CHECK WAS ACCOMPLISHED.