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 iOS 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.
On the Other screen, select “Add Mail Account.”
In the new screen, you will enter:
Select “Next” to get to the full settings. Make sure that at the top of the new screen the type of account highlighted is IMAP.
Enter the incoming and outgoing server names, the username in firstname.lastname@example.org\sharedmailboxalias format and your password then click Next. The mailbox is now ready to use.