ALT UNDERSHOT WHEN THE CREW OF AN A320 FAILS TO MAKE AN ALT XING RESTR AT PAYNT INTXN FOR AN APCH TO PHX; AZ.

Narrative

INBOUND TO PHOENIX; AZ. ON THE ARLIN 3 ARR; WE INADVERTENTLY CROSSED THE 'PAYNT' INTXN AT 11700 FT INSTEAD OF THE ASSIGNED 11000 FT. THIS OCCURRED DUE TO MY ERROR IN INSERTING INTO THE FMGS THE ALT ACCIDENTALLY AT THE NEXT WAYPOINT (ARLIN); WHICH WAS 8 NM BEYOND 'PAYNT.' AT ABOUT 3 1/2 NM FROM PAYNT; THE CTLR ASKED US IF WE WERE GOING TO MAKE THE RESTR. I IMMEDIATELY INCREASED OUR DSCNT RATE. HOWEVER; WE STILL CROSSED IT 700 FT HIGH. THE CTLR THEN HANDED US OFF TO PHOENIX APCH WITHOUT FURTHER COMMENT. TO MY KNOWLEDGE; THERE WERE NO SEPARATION ISSUES WITH ANY OTHER ACFT. CONTRIBUTING TO THIS INCIDENT WAS THE LACK OF CREW XCHK OF MY ALT ENTRY INTO THE FMGS. THE FO WAS STILL 'OFF' ON THE OTHER RADIO TALKING TO PHOENIX OPS CONCERNING OUR GATE ASSIGNMENT; ETC. NORMALLY; THIS FUNCTION IS ACCOMPLISHED PRIOR TO THE BEGINNING OF DSCNT. HOWEVER; THIS TIME; IT OCCURRED LATE; BECAUSE OF INTERFERENCE ON THE PHX ATIS FREQ OF 121.2. IN THE VICINITY OF THE BLH VOR (BLYTHE); THERE IS A TWR OR ARPT TA ON THE SAME FREQ AS THE PHX ATIS; AND HAS BEEN THERE FOR MANY YRS. OUR COMPANY HAS BEEN AWARE OF IT; AND IN THE PAST; HAS ASKED US TO RPT IT TO ATC. IN FACT; I HEARD 2 OTHER ACFT RPT IT TO ZAB ON THIS DAY. WHAT THIS DOES IS DELAY OUR RECORDING OF THE ATIS AND CALLING 'IN RANGE' TO OPS UNTIL WE ARE IN THE DSCNT. PRIOR TO DSCNT; I HAD THE CORRECT 'PAYNT;' 11000 FT RESTR; CORRECTLY INSERTED INTO THE FMGS AND XCHKED BY THE FO. AFTER OBTAINING THE ATIS INFO IN THE DSCNT; I HAD TO CHANGE THE PREVIOUSLY INSERTED RWY IN THE FMGS; WHICH DELETES ALL PREVIOUSLY ENTERED ALT RESTRS FOR THE ARR. I THEN RE-INSERTED THE 11000 FT ENTRY AT THE WRONG WAYPOINT. BECAUSE THE FO WAS STILL 'OUT OF THE LOOP;' HE DID NOT SEE OR CHK MY ENTRY. MY ERROR WAS TO NOT INTERRUPT HIM FOR THIS XCHK. WHILE THE RESPONSIBILITY FOR THIS INCIDENT IS ENTIRELY MY OWN; I WOULD LIKE TO SEE THE FREQ DUPLICATION OF 121.2 IN THE VICINITY OF THE BLH VOR BE RECTIFIED. FORCING US TO DO MANY FUNCTIONS LATE IN THE DSCNT ON THIS HEAVILY TRAVELED RTE (LAX; ONT; LGA; SNR; TO PHX) PRESENTS US WITH AN UNNECESSARILY HIGH WORKLOAD AND INCREASED CHANCE OF THESE TYPES OF ERRORS.