Click Reporting > Calls to see the number of calls made, conversations, and received calls.
In the top right, you can adjust the time period.
Note: Call reporting requires that at least one user in your account has the paid calling add-on.
On the People screen, you can enable columns for last call, calls made, calls received, first call time, and total talk time.
You can filter these columns by Talk Time > 5 mins and Last Call more than 7 days ago for a list of contacts to follow up.