Add a Office 365 Shared mailbox on an iPhone using IMAP
Go to Settings >
Add Account > Other
Add Mail Account
Name: [Users Name]
Email: [Shared Mailbox Email Address]
Password: [Users Main 365 Password]
Next
Incomeing Settings –
Hostname: outlook.office365.com
username: [Users main email address]/shared mailbox name before the @ sign]
Password: [Users Main 365 Password]
Outgoing Settings –
Hostname: smtp.office365.com
Username: [Users main 365 email address]
Password: [Users Main 365 Password]
Next
Email Account has now been setup