B757 CREW MISUNDERSTANDS HOLDING INSTRUCTIONS AT CANNY INTXN.

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FLT SCHEDULED FOR XA12Z DEP DELAYED FOR GND STOP INTO PHL FOR 2 HRS DUE TO HVY TSTMS AT PHL. FLT UNEVENTFUL PRIOR TO ARR SEGMENT; CTLRS ADVISING NO DELAYS INTO PHL. JUST AS WE ARRIVED AT OTT ON THE DUPONT 4 ARR; CTLRS CAUGHT OFF GUARD BY A SUDDEN STOPPAGE AGAIN INTO PHL. THERE WERE MANY AIRPLANES PREVIOUSLY DELAYED AS WE WERE ALL CULMINATING ON THE ARR AND THE CTLRS WERE SCRAMBLING TO ASSIGN HOLDING INSTRUCTIONS. EACH SUBSEQUENT CTLR HAD NEW HOLDING INSTRUCTIONS AT NON PUBLISHED RADIAL/DME HOLDING FIXES. THERE WAS A GOOD DEAL OF CONFUSION FROM MOST COCKPITS. HOLDING INSTRUCTION ASSIGNING US A HOLD BASED ON THE ENO 226 DEG RADIAL THAT WE UNDERSTOOD TO ORIGINATE AT ENO AND READ BACK THAT UNDERSTANDING. THE HOLDING FIX WAS LOADED INTO THE FMC AT WHICH TIME WE QUESTIONED THE INSTRUCTION AND ATTEMPTED TO QUERY THE CTLR BUT DUE TO CONGESTION ON THE FREQ WERE UNABLE TO GET CLARIFICATION UNTIL WE WERE PAST THE INTENDED HOLDING FIX (CANNY). AN IMMEDIATE R TURN PLACED US BACK INTO HOLDING WITH NO APPARENT OR ADVERTISED PROB. THIS MISUNDERSTANDING OCCURRED IN MY OPINION DUE TO THE CTLR'S LACK OF A SPECIFIC HOLDING FIX. THIS WAS OCCURRING AT NIGHT IN ACUTE TSTM ACTIVITY AND CONTINUING CHANGING INSTRUCTIONS. THE CTLRS WERE SATURATED AND THE FREQS WERE SATURATED. A QUICKER REALIZATION OF THE PROB ON OUR PART MAY HAVE ALLEVIATED THE SITUATION BUT WE WERE NEARLY ON TOP OF THE FIX WHEN HOLDING INSTRUCTIONS WERE RECEIVED AND AT THAT TIME COM WITH THE CTLR WAS INHIBITED DUE TO CONGESTION.