This is the 11997th most frequent Russian word.
звонков
"Звонков" means "of calls" (genitive plural form of "звонок").
Here, 'звонков' is the plural genitive form of the word 'звонок' and is used to refer to calls in the sense of 'time of the received calls'.
Мне нужно записать время поступивших звонков.
I need to record the time of the received calls.
In this sentence, 'звонков' also takes the plural genitive form to indicate the calls processed or handled by the operator.
Работа оператора колл-центра включает обработку звонков.
The job of a call-center operator includes handling calls.
Again, 'звонков' is in the plural genitive form, used in expressing the quantity related to calls.