How can I connect my Phone with a Shared Mailbox?
Shared Mailboxes don't have their 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 shared contacts or shared calendar folders.
In order to sync Shared Mailboxes with your own or others (via ExMixedFolders) you have to use Impersonation when you connect to the mailbox.
Since version 1.34 of ExMixedFolders the is a second way of accessing the shared folders. Now the folderbrowser can show all mailboxes where the user is a member of.