VFR C172 TRANSITIONING PHX CLASS B AIRSPACE AT 4500 FT EXPERIENCED NMAC WITH UNRPTED OPPOSITE DIRECTION TFC.

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I HAD DEPARTED CHD FROM RWY 22R ENRTE TO PRESCOTT; AZ; AND CHOSE TO REQUEST CLRNC THROUGH THE PHX CLASS B AIRSPACE NBOUND VIA THE VFR TRANSITION RTE E OF THE PHX ARPT. THE FIRST CTLR I CONTACTED AT PHX APCH CLRED ME INTO THE CLASS B AIRSPACE; INSTRUCTED ME TO 'REVERSE COURSE; FLY DIRECT TO THE INTERSTATE; THEN N BTWN THE INTERSTATE AND THE RWY THRESHOLDS' FOR THE E TRANSITION. AS I CONTINUED NBOUND ALONG THE TRANSITION RTE JUST SE OF THE PHX ARPT; I WAS HANDED OFF TO ANOTHER CTLR; WHO; AFTER CLARIFYING MY INTENTIONS OF AN ENRTE ALT OF 8500 FT; INSTRUCTED ME TO 'MAINTAIN VFR AT 4500 FT.' I CONTINUED ALONG THE E TRANSITION AT THAT ALT (4500 FT) WHEN I BECAME AWARE OF ANOTHER ACFT THAT APPEARED TO BE AT MY 12 O'CLOCK POS AND SOME DISTANCE AWAY. AT THAT TIME I HAD JUST PASSED THE RWY THRESHOLDS AT PHX. I FIRST SPOTTED THE OTHER ACFT'S LNDG LIGHT; WHICH DID NOT ALARM ME; DUE TO THE FACT THAT I HAD FLOWN THROUGH PHX'S AIRSPACE A NUMBER OF TIMES IN THE EVENING AND AT NIGHT PRIOR TO THIS FLT; AND IT WAS NOT UNCOMMON ON A BUSY EVENING TO FLY IN CLOSE PROX TO OTHER AIR TFC THAT WAS NOT ON A 'COLLISION COURSE' AND OBSERVE THEIR LNDG LIGHTS. I CONTINUED TO MONITOR THE ACFT AS I AWAITED POSSIBLE VECTORS AWAY FROM THE TFC FROM PHX APCH. IT WAS APPARENT TO ME THAT TFC WAS RELATIVELY LIGHT IN THE PHX AREA THAT EVENING; AND THE SPECIFIC CTLR HANDLING MY FLT SEEMED VERY UNHURRIED AND NOTICEABLY RELAXED. THE FREQ I WAS COMMUNICATING ON WAS UNCONGESTED AND ESPECIALLY QUIET; CONSIDERING IT IS USED FOR VIRTUALLY ALL LOW ALT TFC IN THE NORTHERN PORTION OF THE PHX CLASS B AIRSPACE. FOR THESE REASONS I BELIEVED THAT I COULD AT THE VERY LEAST EXPECT A TA; AND WITH RESPECT TO THE COURSE OF THE OTHER ACFT; VECTORS AWAY FROM THE TFC AS WELL. AS THE ACFT CONTINUED APCHING; APPARENTLY ON THE E TRANSITION HEADED SBOUND; I REALIZED THE ACFT WAS HEAD-ON WITH ME AS HIS WINGTIP NAV LIGHTS CAME INTO VIEW. AT THIS POINT; I BECAME CONCERNED AND; UNSURE OF THE CTLR'S AWARENESS OF THE SITUATION; BEGAN A SLOW DSCNT TO AVOID THE OTHER ACFT. PRIOR TO AND DURING THE DSCNT; THE APCH CTLR NEVER ADVISED ME OF THE HEAD-ON TFC; AND I DO NOT RECALL HEARING CONVERSATION BTWN THE CTLR AND THE ONCOMING TFC DURING MY COM WITH THE CTLR ON THAT FREQ. DURING THE DSCNT; I NOTICED THE RATE AT WHICH THE WINGTIP NAV LIGHTS OF THE OTHER ACFT BEGAN TO APPEAR DIVERGING; AND I REALIZED THAT THE OTHER ACFT WAS FAST APCHING. AT THIS; I IMMEDIATELY PITCHED THE NOSE DOWN AT A STEEPER ANGLE AND WATCHED THE ACFT AS IT PASSED ABOVE ME AND NARROWLY MISSED MY R WING. I BELIEVE THAT THE TFC WAS IN A SLIGHT DSCNT AS HE PASSED OFF OF MY WING. AFTER THE ACFT PASSED TO MY REAR; I CLBED BACK TO MY ASSIGNED ALT OF 4500 FT FROM AN ALT OF 4300 FT AND CONTINUED NBOUND ALONG THE E TRANSITION. STRANGELY ENOUGH; THE CTLR NEVER COMMENTED TO EITHER MYSELF OR THE SEMINOLE ABOUT THE OCCURRENCE; OR MY DEV FROM 4500 FT. FROM MY PERSPECTIVE; I BELIEVE THAT ALTHOUGH I AVOIDED THE OTHER ACFT; EARLIER DETECTION OF A HEAD-ON COURSE WITH THE TFC AND A FASTER AND MORE DELIBERATE RESPONSE; COMBINED WITH A TURN; WOULD HAVE PROVIDED BETTER SEPARATION BTWN MYSELF AND THE SEMINOLE. ADDITIONALLY; AVOIDANCE MEASURES TAKEN BY THE SEMINOLE WOULD HAVE AIDED SEPARATION. ALSO CONTRIBUTING TO THE NMAC WAS THAT I FAILED TO QUERY THE CTLR ABOUT THE ONCOMING TFC AFTER I NOTICED IT; AND THAT I EXPECTED AN ADVISORY AND VECTORS FROM PHX APCH. AT THE TIME OF THE OCCURRENCE; THE ACFT I WAS FLYING WAS EQUIPPED WITH A LNDG LIGHT IN THE NOSE OF THE ACFT; WINGTIP AND TAIL POS LIGHTS; AND A RED ANTI-COLLISION BEACON ATOP THE STABILIZER OF THE ACFT; ALL OF WHICH WERE OPERABLE AND LIGHTED. I AM UNSURE AS TO WHEN; OR IF; THE SEMINOLE DETECTED ME AS TFC; DESPITE THESE PRECAUTIONS. I STILL QUESTION WHY THE PHX APCH CTLR DID NOT ATTEMPT TO CONTACT MYSELF OR THE SEMINOLE REGARDING A POSSIBLE CONFLICT/COLLISION; AND WHY SECONDS AFTER THE OCCURRENCE HE CONTINUED TO ISSUE INSTRUCTIONS TO OTHER ACFT IN THE SAME RELAXED TONE; AS THOUGH NOTHING HAD HAPPENED.