B737 FLT CREW RECEIVED TAXI INSTRUCTIONS FOR RAMP ENTRY AFTER LNDG. INSTRUCTIONS INCLUDED SPOT NUMBER FOR CONTACTING RAMP CONTROL. SPOT NUMBERS ON ONE COMMERCIAL CHART PAGE DO NOT COINCIDE WITH SPOT NUMBERS ON ANOTHER COMMERCIAL CHART PAGE.

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AFTER LNDG WE CROSSED RWY 9L NBOUND ON TXWY E AND WERE; I THOUGHT; TOLD TO TAXI ON TAXI K AND ENTER THE RAMP AND CONTACT RAMP AT SPOT X. THIS IS WHAT I THOUGHT I HEARD AND READ BACK THE INSTRUCTIONS AS SUCH. THE CTLR DIDN'T CORRECT THE ERROR UNTIL WE WERE HALF WAY BTWN TXWY E AND K3. BOTH CAPT AND I THOUGHT THE INSTRUCTIONS WERE ODD; BUT IT IS PHL. THERE ARE 3 SPOT X'S ON MY COMMERCIAL CHART FORM AND I FIGURED THEY WERE BRINGING US IN FROM THE S SIDE OF THE RAMP FOR SOME SPECIFIC REASON. AFTER THE CTLR CORRECTED THE ERROR; WE DID A 180 DEG TURN AND RETURNED ON TXWY K; THEN TO SPOT X. THE SITUATION WAS CORRECTED AND THERE WAS NO CONFLICT WITH ANY OTHER TFC. CLEAN UP THE COMMERCIAL CHART PAGES TO REFLECT LESS CONFUSION ON WHICH SPOT X IS 'THE' SPOT X. ALSO HAVE THE CTLRS SPEAK UP WHEN A CLRNC IS READ BACK INCORRECTLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT HE HAD BEEN PREVIOUSLY CAUTIONED ABOUT THE CONFUSING TAXI SITUATION AT PHL. WHEN TAXI INSTRUCTIONS WERE ISSUED; THE FLT CREW REFERENCED THE COMMERCIAL CHART PAGE AND BELIEVED THAT THEY WERE TO APPROACH THE ASSIGNED SPOT FROM THE SOUTH. THE CONTROLLER CLARIFIED THE TAXI CLEARANCE; AND THE FLT CREW REVERSED THEIR TAXI.