Yes, if you have enabled the relevant setting for the OWA MetaCompliance Phish Mail plugin ('EnableSharedMailbox'), users can report emails from a Shared Mailbox.

Prerequisites

This functionality is available only in the OWA version of the MetaCompliance Phish Mail plugin.

To utilise this setting:

• The Shared Mailbox must be added to the user's Outlook profile as an additional account.
• The user must also have delegated the Send As permission for the Shared Mailbox. 

Permissions

To support Shared Mailbox reporting, the following additional permissions must be enabled in your Office 365 Admin Centre:

• Mail.ReadWrite.Shared
• Mail.Send.Shared

Outlook via Web 

• Accessing a mailbox using Open another mailbox in Outlook Web is not supported.

Outlook via Mobile

• Accessing a mailbox using the Add Shared Mailbox option on mobile devices is not supported.

Installation

• If the Phish Mail plugin has already been deployed to your users, a new version of the plugin will be required to utilise this setting. Please contact our Support team to arrange the update.
• If you are not currently using the Phish Mail plugin and are interested in this functionality, then please speak with your MetaCompliance representative and ensure the EnableShareMailbox setting is set to true.