welcome to airtable community.
I can think 2 ways to do it:
create one column (column A) with numeric data type, this will include the number you are looking for.
Then create new column (column B) with a formula that will sum up with +1 the previous column.
Then in Zap give this setting: When a new call is incoming then update the record by adding in column A the content of column B.
Last but not least create an automation that will delete the content of column A every night for instance to start the counter from the beginning.
On every new incoming call create a new record line so then you will be able to count the new lines be date to find the number of incoming calls on specific days.
Please let me if those solutions work for you and for any further question please feel free to text back to community.