To access the full Billing and Contact page (or Contact Management Portal) for a client in the Web Portal, go to CRM > All Contacts > click on the ID number or the Arrow for the Billing / Contact you wish to access.
This will take you to the Contact Management Portal for the specified contact, where you will also be able to access the communications, activity, and history information.
Note: If you would like to keep your contacts list in a browser tab, you can right-click on the ID or Arrow, and choose to open the link in a new tab.