DH8 CREW HAD LESS THAN LEGAL SEPARATION FROM UNKNOWN ACFT AT PHX.

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WHILE ON DSCNT FROM 9000 FT TO 7000 FT MSL AT APPROX 30 MI NE OF PXR VOR; ON ATC APCH CTL VECTOR 180 DEG ASSIGNED HDG; THE CAPT (PNF) NOTED POP-UP TFC ON THE TCASII DISPLAY (IMC PREVAILED). TFC RANGE WAS 2-3 MI AT 12 O'CLOCK POS AND 500 FT LOWER (TFC WAS POSSIBLY IN LEVEL CRUISE). WE WERE DSNDING AT 1000 FPM. I ASKED THE PF (FO) TO TAKE APPROPRIATE ACTION TO AVOID TFC CONFLICT. THE FO THEN ADDED PWR AND LEVELED OFF THE DSCNT. APPROX 3 SECONDS LATER; WITH TFC ON TCASII NOW AT OUR ALT; THE TCASII GAVE A RESOLUTION ALERT TO CLB AT 1500 FPM. THE FO AGAIN ADDED PWR AND CLBED ABOVE THE TFC. I ADVISED ATC OF THE RESOLUTION ALERT. AND THE CLB TO AVOID CONFLICT. THE APCH CTLR SEEMED UNCONCERNED WITH OUR TFC NEAR MISS IN IMC; STATING ONLY 'THE TFC HAD JUST APPEARED ON HIS RADAR SCOPE.' I AM CONCERNED WITH PHX APCH CTL'S TREATMENT OF TURBOPROP COMMUTER ACFT AS SECOND CLASS CITIZENS. WHY WERE WE VECTORED OFF OF THE ARR (FOSSIL 4) AT AN ALT AND POS CLR OF CLASS B AIRSPACE? THIS IS A VERY COMMON PRACTICE IN PHX AIRSPACE. THIS POOR PROC IS UTILIZED TO CREATE SPACING BTWN TURBOPROP AND JET ARR TFC. IT MUST STOP FOR COLLISION AVOIDANCE SAFETY REASONS. HOW IS IT POSSIBLE FOR ANOTHER ACFT TO BE IN OUR AIRSPACE IN IMC AND NOT BE UNDER ATC CTL? IN 11000 HRS OF FLT TIME I HAVE NEVER RESPONDED TO AN RA. I NOW KNOW THAT TCASII IS INDEED THE PLT'S BEST FRIEND WHEN IN IMC TFC NEAR MISS SITS. THANK YOU FOR A VALUABLE PIECE OF EQUIP.