B737 FLT CREW FAILS TO COMPLY WITH ATC DIRECTED ALT XING RESTR INBOUND TO PHX.

Narrative

CAPT HAD GONE TO THE BACK; AND ATC HAD CLRED US TO DSND TO CROSS 55 MI N OF BERYL INTXN AT FL290. WE WERE AT FL330. I PUT FL290 IN THE FMC AND THE MCP. SOMEHOW BECAME DISTR AND DID NOT PUSH THE EXECUTE BUTTON. A FACTOR HERE WAS THAT THE LIGHT SWITCH WAS STILL IN DIM FROM THE PRE-DAWN TKOF; AND THE EXECUTE LIGHT WAS NOT VERY VISIBLE. ANYWAY; THE FMC NEVER STARTED DOWN AND I DID NOT NOTICE; UNTIL ATC ASKED IF WE WERE GOING TO MAKE THE XING RESTR. I WENT TO LEVEL CHANGE AT THAT TIME; BUT STILL DID NOT MAKE IT DOWN BY THE XING FIX. NO FURTHER COMMENTS FROM ATC. ABOUT THE TIME ATC WAS ASKING IF WE WERE GOING TO MAKE THE RESTR; THE CAPT CALLED AND CAME BACK UP FROM THE BACK. FACTORS CONTRIBUTING TO THIS EVENT WERE A FAILURE TO COMPLETE THE ALT CHANGE TASK BECAUSE OF SOME DISTR THAT I DON'T REMEMBER WHAT IT WAS; A DIM EXECUTE LIGHT THAT MIGHT HAVE REMINDED ME TO FINISH THE TASK; AND NOT HAVING ANOTHER PLT TO CATCH MY MISTAKE. SUPPLEMENTAL INFO FROM ACN 593879: WHILE I WAS ABSENT FROM THE FLT DECK TO USE THE RESTROOM; A CLRNC HAD BEEN ISSUED TO CROSS 50 NM NW OF DRAKE (N OF PHX) AT FL290. WHEN I RETURNED FROM THE RESTROOM; I HAD NOT BEEN INFORMED OF THE ATC ISSUED XING RESTR. AS I STRAPPED IN AND PUT MY HEADSET ON; CTR REQUESTED THAT WE START OUR DSCNT IMMEDIATELY TO COMPLY WITH THE CLRNC. AS I LOOKED AT THE NAV DISPLAY; I NOTICED THAT THE FO HAD PROGRAMMED A FIX OF DRK/01 WHICH TURNED OUT TO BE THE XING RESTR POINT. WHEN ATC CALLED TO DIRECT THE IMMEDIATELY DSCNT; THE ACFT WAS PASSING THE POINT FOR THE XING RESTR AT FL330.