ATCT LCL CTLR AT PHX LOST SEPARATION BTWN 2 IFR DEPS OFF PARALLEL RWYS.

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I CLRED THE B733 FOR TKOF. MY ACFT WAS FOLLOWING THE WW24 OFF THE PARALLEL RWY. THE WW24 WAS CLBING OUT AT 200 KTS AND THE B733 WAS CLBING OUT AT 180 KTS. I SHIPPED THE B733 TO DEP CTL. I LOOKED AT MY D-BRITE RADAR AND FELT I HAD 3 MI OF DEP SEPARATION (LATER INVESTIGATION SHOWED MY DEP SPACING WAS 2.94 MI). SUBSEQUENTLY; 5-6 MI E OF THE ARPT THE B733 WAS CLBING OUT AT 240 KTS AND THE WW24 WAS CLBING AT 200 KTS. EVENTUALLY THE DEP CTLR'S SEPARATION DECREASED TO 1.66 MI AND 500 FT. SEVERAL CASUAL FACTORS CAME TO PLAY. BOTH ACFT WERE NOT FLYING DEP PROC (DP) CORRECTLY AND THE DEP CTLR DID NOT RECOGNIZE THE DETERIORATING CONDITION. THE DEP PROCS INITIAL HEADING IS 080 DEGS; THE WW24 WAS 12 DEGS S OF THE DEP PROC (DP); THE B733 WAS CLBING OUT FASTER THAN COMPANY REQUIREMENTS; THE WW24 WAS GIVEN 020 DEGS TO RESUME THE DEP PROC (DP); THAT'S WHERE THE SEPARATION DECREASED TO 1.66 MI AND 500 FT. I BELIEVE HAD BOTH ACFT BEHAVED PROPERLY ON INITIAL CLBOUT; MY 2.94 MI WOULD'VE CONTINUED TO INCREASE TO 3+ MI. ALTHOUGH; I TOLD THE B733; THAT HE'D BE FOLLOWING A WW24 OFF THE S RWY; I DID NOT GO BACK AND APPLY VISUAL SEPARATION; BECAUSE I FELT I HAD THE MINIMUM 3 MI OF RADAR DEP SEPARATION. THE LESSON LEARNED; IF YOU'RE GOING TO USE MINIMUM SEPARATION ALSO APPLY VISUAL SEPARATION ON THE TRAILING ACFT TO THE ONE OUT FRONT.