CHANGE OF RWY ASSIGNMENT TO A PREVIOUSLY CLOSED RWY DURING AN ARRIVAL TO PHL WITH UNFORECAST WX LEADS TO A DEV FROM TRACK AND GLIDESLOPE.

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THE WEATHER WAS NOT THE 7 SM VISIBILITY EXPECTED; BUT WAS ACTUALLY GETTING FOGGY DUE TO A ZERO TEMPERATURE DEW POINT SPREAD. WE SENT DISPATCH AN ACARS AS SOON AS WE HEARD THAT OTHER AIRCRAFT AHEAD OF US WERE BEING DIRECTED TO HOLD AT BUNTS AS PUBLISHED; AND INFORMED THEM OF OUR FUEL ON BOARD. WE HAD NO ALTERNATE SINCE OUR FORECAST DID NOT REQUIRE ONE. RWY 27R WAS REPORTED CLOSED IN THE ATIS AND WE PLANNED FOR AND BRIEFED ILS RWY 27L. AS SOON AS WE RECEIVED A DESCENT AND HOLDING INSTRUCTIONS; I CONTACTED DISPATCH ON THE RADIO AND ADVISED THEM OF THE SITUATION. I INQUIRED IF THEY HAD RECEIVED MY MESSAGE AND THEY ACKNOWLEDGE THEY DID; BUT I WONDERED WHY NO REPLY WAS RECEIVED. AS WE ENTERED THE HOLD; I DIRECTED THE FIRST OFFICER TO MONITOR THE #1 RADIO WITH ATC COM AND I WOULD BE OFF CREATING A PLAN OF ACTION IN CASE OF A DIVERT SITUATION. I AGREED ON A BINGO FUEL WITH DISPATCH AND THEY CALCULATED FOR ME THE FUEL BURN AND TIME TO DIVERT TO EWR. I TOLD THE FO TO PASS ON TO ATC THAT THE SECOND HOLDING TURN; WHICH WE WERE ON; WAS THE LAST AND WOULD BE DIVERTING UNLESS WE WERE CLEARED IN FOR THE APPROACH. WE WERE TOLD TO EXPECT A TURN INBOUND AFTER LEAVING THE FIX; AND UPON REACHING THE FIX; WE RECEIVED VECTORS FOR A DOWNWIND. THIS SEQUENCE OF EVENTS MADE ME MISS THE RADIO CALL FOR THE RUNWAY CHANGE TO RWY 27R; AND DURING VECTORS WE STILL HAD RWY 27L IN THE FMS. IT WASN'T UNTIL APPROACH CLEARED US DIRECT JALTO INTERSECTION AND CLEARED US FOR THE APPROACH; THAT I REALIZED HE MEANT THE RWY 27R ILS APPROACH. I QUESTIONED THE FO SINCE HE CORRECTLY ACKNOWLEDGED DIRECT JALTO. I CAME ON THE RADIO AND VERIFIED OUR CLEARANCE TO BE DIRECT JALTO ILS RWY 27R. AT THIS TIME WE WERE INTERCEPTING THE RWY 27L LOCALIZER AND I ADVISED TOWER THAT WE WERE MAKING A POSITIVE CORRECTION TO THE ILS RWY 27R. IN ORDER TO DO THIS I DISCONNECTED THE AUTOPILOT AND CORRECTED TO JOIN THE LOC AND GS; CAUSING ME TO ME TO GO BELOW THE GLIDE PATH WHILE ON THE LOC; BUT STILL OUTSIDE THE FAF. WE RECEIVED A RADIO CALL TO VERIFY OUR ALTIMETER SETTING OF 29.98; WHICH WE HAD SET; WHICH WAS PROMPTED BY OUR DEVIATION. THE FO CHANGED THE FMS TO REFLECT THE CORRECT APPROACH; VERIFIED THE NEW ILS FREQUENCY AND MINIMUMS WERE SET AND COMPLETED THE LANDING CHECKLIST. OUR LANDING WAS UNEVENTFUL BUT I FELT THINGS COULD HAVE GONE A LOT BETTER IF I WOULD HAVE REALIZED THE CLOSED RWY WAS NOW THE ARRIVAL RWY; AND I SHOULD HAVE NOT WORRIED ABOUT OUR FUEL SITUATION ONCE I COMMITTED TO THIS AIRPORT. RADIO COM WAS VERY BUSY DUE TO THE WX AND VARIOUS AIRPLANES DIVERTING; AND WE DID NOT HEAR THE PREVIOUS AIRPLANE RECEIVING THE JALTO CLEARANCE. I DECLARED MIN FUEL BUT LOOKING BACK SHOULD HAVE DECLARED EMERGENCY FUEL AND RECEIVED PRIORITY HANDLING.