To access the full Billing and Contact page for a client in the Web Portal, go to CRM > Contacts > click on the ID or the Arrow for the Billing / Contact you wish to access.
This will take you to the main Billing / Contact page, where you will also be able to access the communications and activity 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.