N Harkawat wrote...
assuming that your 3 digit area code is in row 1 between A1:D1 and the phone
number is between B1:D6000
and "another cell" holding the area code is cell F1 and phone number in F2

=IF(ISNA(INDEX(OFFSET(A2,,MATCH(F1,$A$1:$D$1,0)-1,6000),
MATCH(F2,OFFSET(A2,,MATCH(F1,$A$1:$D$1,0)-1,6000),0))),"N","Y")

will give a Y or N depending whether phne number exists
....

The volatile OFFSET call isn't needed for this. It could be done with

=IF(ISNUMBER(1/COUNTIF(INDEX($A$2:$D$6000,0,MATCH(F1,$A$1:$D$1,0) ),F2))
,"Y","N")

Another advantage is that if rows with new phone numbers were inserted
between rows 2 and 6000, the range reference in the INDEX formula will
automatically expand to include them. The OFFSET formula would require
manually changing the 6000 figures.