Outlook for iOS / Outlook App (Android)
it is not (yet) possible to Access Shared Mailboxes on Exchange on-premise or Exchange Online.
One Needs to Setup OWA for iOS simulaneously to Outlook for iOS.
OWA for iOS imho is a deprecated software not supporting all features like Outlook for iOS (e.g. Apple Watch etc.).
Please implement access to shared mailboxes also for Outlook App on iOS or Android.
It has been confirmed by the O365 Business Support that this feature is missing.
Shared mailboxes access via iOS for allmost any organisations is a must.
Often shared/funktion mailbox is needed when away from office and only option is app from phone
Nick Shortal commented
Shared mailboxes access via iOS for large organisations is a must. Often staff that are out an about need to the ability to react quickly to an email request.