If you receive an email you think is suspicious, you can now report it directly from within Outlook. This works for Outlook on Android, iPad, iPhone, Mac, PC, and in webmail. When you report a message it will be analyzed, and if it is malicious the message will be removed from any mailboxes in which it was delivered. Reporting the message will also delete it from your Inbox.

When viewing a message in webmail, also called Outlook Web Access / OWA, there is a set of three dots next to the reply and forward controls:

Click on those dots to open the options for that message and select the Report Phish button:

You will see a confirmation appear when the report is sent.