A ACR PLT APCHING PHX RPTS AN RA AND CLASS D AIRSPACE ENTRY ON VISUAL APCH TO RWY 26 AT 3500 FT. RPTR COULD NOT DEFINE THE PHX CLASS B AIRSPACE BOUNDARY.

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BEING VECTORED FOR A VISUAL APCH TO RWY 26 IN PHX. APPROX 15 MI FROM PHX WE WERE CLRED DOWN TO 4000 FT AND ASKED IF WE HAD THE ARPT IN SIGHT. WHEN WE REPLIED THAT WE DID; WE WERE CLRED FOR THE VISUAL APCH TO RWY 26. I PLANNED TO CONTINUE MY DSCNT TO 3100 FT FOR THE POWER PLANT VISUAL. AT APPROX 3500 FT; APCH CTL ADVISED THAT FOR FUTURE REF WE NEEDED TO BE CAREFUL ON THE APCH BECAUSE WE HAD ENTERED CLASS D AIRSPACE ON OUR DSCNT. AT THE SAME TIME WE RECEIVED A TCAS TA FOR AN ACFT AT 3000 FT. WE STOPPED OUR DSCNT THEN RECEIVED A TFC WARNING FROM APCH CTL AND WERE TOLD TO IMMEDIATELY STOP OUR DSCNT. THE TCAS WARNING THEN TURNED TO AN RA AND INSTRUCTED US TO CLB. WE COMPLIED WITH THE RA; CLBED TO 4000 FT; CLRED THE TFC AND CONTINUED THE APCH TO LNDG UNEVENTFULLY. THE CAUSE OF THIS EVENT WAS MY LACK OF KNOWLEDGE CONCERNING THE AIRSPACE LAYOUT IN THE PHX AREA. I SHOULD HAVE REVIEWED THE COMMERCIAL CHART AND HAVE BEEN MORE AWARE OF MY POS. I FEEL A CONTRIBUTING FACTOR IS THE LACK OF FIXED POS MARKERS TO DEFINE THE BOUNDARIES OF THE PHX CLASS B AIRSPACE. THE FLOOR OF THE CLASS B DROPS TO 3000 FT BUT ISN'T CLRLY DEFINED.