Calculate who has the most repeat calls in the call center

Then you can use something like...

In E2:

Formula:

=IF(D2="Y",INDEX($B$1:B1,MAX(IF($C$1:C1=C2,ROW($C$1:C1)))),"")

Confirmed as Array formula (CTRL + SHIFT + ENTER)

See attached.
Note: I've edited Row 24 to have same CustomerPhone# as Row 26 & 35 to demonstrate Case where customer called 3 times in a 2 week period.