Site or shared mailboxes don't have their own logon but they can be opened in an Outlook profile using the credentails of anyone who has Full Access permission to the mailbox. Unfortunately, when you use your credentials to set up an Exchange account on a smartphone, it opens your mailbox, not the shared mailbox. These instructions will show you how to setup access to shared mailboxes on your Android device.
Enter the shared mailbox's display name and SMTP address on the first screen. Type the user's email password in the password field. Click Next.
Enter the server name and port settings, the username in email@example.com\sharedmailboxalias format and your email password. Click Next.
Enter the outgoing server name or port settings.
(If needed, use your username and password for Outgoing authentication.) -Should not be needed.