Click on the phone you would like to view in the list of phones on the left side of the screen.
That phone's list entry will expand. Click on the link labeled Texts, Calls & Apps.
A page showing that family member's texting activity will appear. Notice there is a tab near the top of the page labeled Calls. Click on it.
A page showing that family member's calling activity will appear. Look at the All Hours box in the lower left side of the page to see how much time that family member spent on the phone in the past week.