How can I connect my Phone with a Shared Mailbox?
Shared Mailboxes don't have ther own username and password set, which does not allow you to connect via ActiveSync from your Phone. But there is a way to connect by IMAP as you can read here.
In this case it's only possible to get the mails, but not any of the folders like contacts or calendar.
In order to sync Shared Mailboxes with your own or others (via ExMixedFolders) you have to use Impersonation.