B737 FLT CREW HAS TCASII TA DURING VISUAL APCH TO PHX.

Narrative

ON RADAR VECTOR DOWNWIND TO RWY 25L ABEAM PHX ARPT AT 6000 FT MSL 210 KTS; APCH CTL INSTRUCTED US TO SLOW TO 180 KTS; THEN DSND TO 4000 FT MSL. NO TFC TO FOLLOW CALL WAS GIVEN. ABEAM THE PWR PLANT AT 5000 FT MSL/180 KTS; APCH CTL CLRED US FOR THE VISUAL APCH AND TO SWITCH TO TWR FREQ. AGAIN; NO TFC TO FOLLOW CALL WAS GIVEN. PNF MADE THE BASE CALL TO TWR AS THE TURN WAS STARTED. PHX TWR ASKED IF WE HAD BEEN TOLD TO FOLLOW TFC. AT THE SAME TIME; I VISUALLY ACQUIRED ACFT Y APCHING THE PWR PLANT ON A STRAIGHT-IN FINAL AT APPROX 3000 FT MSL. I BEGAN TO LEVEL ABOVE 4000 FT MSL AND SLOWED THE TURN TO LAG BEHIND ACFT Y. TWR ASKED IF WE COULD FOLLOW ACFT Y TO LAND ON RWY 25R. PNF REPLIED IN THE AFFIRMATIVE. WE THEN FULLY CONFIGURED THE ACFT FOR LNDG ON BASE; LAGGED BEHIND ACFT Y TO ROLL OUT ON FINAL FOR RWY 25R. TFC LNDG ON RWY 26 WAS ALSO VISUALLY ACQUIRED WHILE ON BASE (ACFT Z); BUT WAS NEVER A FACTOR SINCE RWY 25R CTRLINE WAS NOT CROSSED. RECEIVED A TCASII TA FROM BOTH ACFT ON BASE LEG. AFTER ROLLING OUT ON FINAL. THE REMAINDER OF THE FLT WAS UNEVENTFUL. A TA TO FOLLOW ACFT Y ON FINAL TO RWY 25L FROM PHX APCH AND BETTER VISUAL LOOKOUT (CLRING OF RWY 25L FINAL) WOULD HAVE PREVENTED A TURN TO BASE AT THAT POINT AND PREVENTED THE TFC CONFLICT.