B727 CREW HAD RWY INCURSION AT LCK.

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FO CALLED FOR TAXI. GND TOLD US TO TAXI TO RWY 23R VIA TXWY D. (PART OF THE NORMAL TXWY TO RWY 23R WAS UNDER CONSTRUCTION; WHICH REQUIRED US TO BACK TAXI DOWN RWY 23R FOR TKOF.) THE FO READ BACK THOSE INSTRUCTIONS PLUS ADDED THE PHRASE 'BACK TAXI INTO POS AND HOLD;' TO WHICH THERE WAS NO RESPONSE FROM GND. THE FO HAD BEEN TO THIS FIELD MANY TIMES. THAT HAD BEEN THE NORMAL TAXI INSTRUCTIONS. THE CAPT AND I HAD NOT BEEN TO THIS FIELD SO WE DID NOT QUESTION THE TAXI INSTRUCTIONS. RELYING ON THE KNOWLEDGE OF THE FO; WE TAXIED TO RWY 23R VIA TXWY D. I WAS IN THE MIDDLE OF MY TAXI 'FLOW CHKLIST' WHEN WE CROSSED ONTO RWY 23R AND AT THAT TIME GND TOLD US TO CONTACT TWR TO BACK TAXI TO RWY 23R. IT WAS THEN WE ALL REALIZED THAT WE SHOULD HAVE HELD SHORT OF RWY 23R. WE CONTACTED TWR WHO THEN INSTRUCTED US TO BACK TAXI INTO POS AND HOLD ON RWY 23R. WE ALL SHOULD HAVE BEEN MORE IN TUNE WHEN THE GND CTLR DID NOT RESPOND TO THE 'ADDED PHRASE' BY FO AND QUESTIONED THE CLRNC FOR CLARIFICATION. NEVER ASSUME NO MATTER HOW MANY TIMES YOU HAVE BEEN TO AN ARPT.