B734 FLC CORRECTLY RESPOND TO PHL LCL CTLR AND TAXI INTO POS FOR DEP WHEN ANOTHER ACR ADVISES TWR THAT THEY THOUGHT THEY WERE NEXT FOR DEP.

Narrative

TWR HAD GIVEN OUR SEQUENCE TELLING US (ACR) TO FOLLOW COMPANY B737 AHEAD. THEY HAD 3 LINES OF ACFT FOR RWY 27L. THERE WAS A B737; SAME DIRECTION ON TXWY S. AS THE ACFT DEPARTED; WE FOLLOWED THE ACFT DIRECTLY IN FRONT OF US UNTIL WE WERE IN THE 'THROAT;' BEING THE ONLY ACFT WITH ACCESS TO RWY 27L. AFTER CLRING THE LEAD B737 FOR TKOF; HE MUMBLED THE CALL SIGN (SOUNDED LIKE XXX). PLEASE NOTE THE USE OF NONSTANDARD VERBIAGE FOR CTLRS IS STANDARD 'XXX; POS AND HOLD.' I ACKNOWLEDGED THE COMMAND SAYING 'ACR XXX; POS AND HOLD RWY 27L;' AND TAXIED INTO POS. LINED UP WITH THE CTRLINE WHEN ANOTHER ACFT CALLED TWR AND SAID; 'TWR ACR YYY IS NOT THE ACFT ON THE RWY.' TWR WAS SILENT; SO I CALLED AND SAID 'ACR XXX IS ON THE RWY.' TWR CLRED US FOR TKOF AND CONTACT DEP. BEFORE SWITCHING TO DEP; WE HEARD TWR TELL THE OTHER ACFT THAT HE HAD SOMEONE OUT OF LINE AND MESSED UP THE SEQUENCE. 1) ALTHOUGH THE CALL SIGNS ARE SIMILAR; THEY WERE NOT CONFUSING TO US; ALTHOUGH TWR MAY HAVE CONFUSED WHICH ACFT WAS ON TXWY S; THEREFORE; NOT THINKING ANYTHING WAS WRONG WHEN WE WERE HOLDING SHORT #1. 2) ACFT YYY SHOULD HAVE SAID SOMETHING AS WE PULLED UP TO THE HOLD SHORT LINE. 3) USE OF ABBREVIATED TERMINOLOGY BY THE TWR DID NOT HELP. 4) USING 3 LINES OF ACFT FOR THE ACTIVE RWY LEADS TO FOLLOWING THE WRONG ACFT. 5) THE SEQUENCE IN PHL IS ALWAYS IN QUESTION. SUPPLEMENTAL INFO FROM ACN 518518: SINCE WE HAD BEEN INSTRUCTED TO FOLLOW THE PREVIOUS ACFT; WE WERE NEXT IN POS FOR THE RWY AND THE ONLY ONE THAT HAD ACCESS TO THE RWY AT THAT POINT. I STILL HAVE NO IDEA OF HOW THE MISCOM TOOK PLACE.