By default, ServiceNow does not display the list of calls for a user in the Details view. To enable it:
Open the Details view for any user.
Click the menu icon at the top left, and navigate to Configure > Related Lists.
In the Related Lists, search for Phone Log->Contact in the left pane (Available) and click > to add it to the right pane (Selected).
Click Save.
View phone calls for the user in this area: