As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO PHX DUE TO THE FLIGHT CREW REPORTING A YELLOW HYDRAULIC SYSTEM RESERVOIR LOW CAUTION ECAM MESSAGE IN FLIGHT. THE AIRCRAFT LANDED SAFELY AT PHX AND TAXIED TO THE GATE UNDER ITS OWN POWER. MAINTENANCE REPLACED THE LOW-LEVEL SWITCH FOR THE YELLOW HYDRAULIC RESERVOIR PER AMM 29-31-41-000-004-A AND ACCOMPLISHED A SATISFACTORY OPS & LEAK CHECK WITH NO ISSUES NOTED.