IFR LR31 landing SDL; experienced a TCAS RA with VFR traffic; reporter alleging ATC's operational practices at P50 need revisions to more positively separate VFR and IFR aircraft.

Narrative

On a flight to Scottsdale we were given the SUNNS6 arrival SSO transition. Prior to entering the Class B airspace we were given a clearance direct IWA direct SDL. Prior to crossing IWA we were given a turn to heading 220. At this point we were at 5000 FT. Then cleared to 4000 FT. As we leveled at 4000 FT we were in very dense traffic (normal for the airspace). We were given a turn to 310 and within a few miles. An ATC traffic advisory of 11 o'clock traffic; 2 miles at the same altitude. We were then given a turn; to the left 10 degrees (toward the traffic). We refused the turn as it would have put us in conflict. We informed ATC of our issue with the turn and they informed us that there was additional traffic that they were trying to work in our same area and that the turn would not put us in jeopardy. We took the turn: new heading 300. There was no problem now as about 1 minute elapsed and the for mentioned traffic was no longer a factor. We were then turned to 350 degrees. This is the standard path for arrivals for satellite airports in PHX. As we approached the PHX airport (crossing the departure end of the east runways) we were told of additional traffic at our 12 o'clock 2 miles 3500 FT. Seconds later we received an RA climb of 1000 FPM. We complied with the RA and upon resolution immediately returned to 4000 FT. The rest of the flight was uneventful. I believe the RA and loss of separation was due to the procedure used to transition VFR and IFR aircraft in PHX airspace. The procedure ATC currently uses is to put IFR traffic on the same routes as VFR traffic and to cross the PHX airport facilitate landing at the satellite airports. As with most high density airports with east - west runways the airspace ends up split along the extended center line causing a need for some sort of north - south transition. In order to reduce the possibility of conflicts I suggest that all satellite airports north of the east - west centerline use the JCOBS arrival with the appropriate transition for aircraft located from a magnetic course of 240 to 120 from SWIRL intersection. This will decongest the airspace over the PHX airport and provide a safer environment for all concerned.