To report a suspicious email in Outlook, select the email and click the Microsoft Report Phishing button in the ribbon. A pop-up will appear with information about phishing and an option to report the email as spam. Click the blue "Report" button to proceed. 

The reported email will be moved to your Deleted Items folder, and a confirmation notification will be sent.  

If you need more help with the Microsoft Report Phishing button in Outlook, please refer to the documentation below.