After you select a message, tap the three vertical dots in the upper right-hand corner of the message.
Scroll down and tap the Phish Alert button.

After you select a message, tap the three vertical dots in the upper right-hand corner of the message.

Scroll down and tap the Phish Alert button.

Select the classification of the email and tap "Phish Alert" at the bottom.

Microsoft Outlook is an email application. In addition to email client services, Outlook includes features for managing calendars, tasks, contacts, and notes, helping users stay organized and productive. Learn how to manage your account, set up your Outlook email signature, specify out of office hours, and much more.

How to Use the Phish Alert Button on the Mobile Outlook App