A320 FLT CREW TAKE EVASIVE ACTION TO AVOID A SEL ACFT ON THE EDGE OF THE PHX CLASS B AIRSPACE.

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DURING DSCNT FROM 12000 FT MSL TO 8000 FT MSL; APCHING 9000 FT MSL ON THE BUNTR 1 ARR; WE HAD JUST TURNED TO A 225 DEG HDG EPR THE ARR PROC WHEN APCH CTL CALLED OUT TFC AT 12 O'CLOCK BELOW US. OBSERVING TFC ON TCASII (WHT; SIGN.) THAT APPEARED TO BE A POTENTIAL CONFLICT; WE REQUESTED RADAR AVOIDANCE VECTOR; AND SLOWED OUR DSCNT. ATC DIRECTED A TURN TO THE R; AND WE COMPLIED. AT THAT POINT; THE TFC IN QUESTION BECAME AN AMBER TCASII ADVISORY; FOLLOWED SHORTLY BY A RED RA 'RESOURCE DSCNT' AND THEN 'MONITOR VERT SPD.' IN CONJUNCTION WITH THE INITIAL RA; WE SIGHTED THE ACFT APPROX 500 FT BELOW US AND SLIGHTLY TO OUR L AT ROUGHLY 8500 FT MSL; AND CONTINUED A SHALLOW R TURN TO INCREASE SEPARATION. ESSENTIALLY; THE RA RECONFIRMED WHAT WE HAD INITIATED. FOLLOWING 'CLR OF CONFLICT;' WE ADVISED ATC THAT WE HAD THE TFC INSIGHT; RECEIVED RADAR VECTORS; RESUMED OUR DSCNT; ADVISED ATC OF OUR RA; AND LANDED UNEVENTFULLY. IN SHORT; THE SYS (ATC; PLTS; TCASII; ETC) WORKED. HOPEFULLY; GENERAL AVIATION IS AWARE OF THE NUMEROUS IFR ARR (AND DEP) CORRIDORS IN AND OUT OF SKY HARBOR.