For a more convenient way to report the mail, there is a way to create a keyboard shortcut in Desktop Outlook.

First, right-click on the Phishing Addon Button and add it to Quick Access Toolbar.

The small icon would appear in the Toolbar in the left top corner.

By pressing Alt the quick access indicator will show which button is assigned for the Report shortcut.

Selecting an email and pressing Alt+3 will report the email