Outlook, not opening can be because of several reasons. Some of the most common reasons are issues with the Outlook service, internet connectivity issues, bugs in the app, app updates, outdated add-ins, defective Outlook PST files, corrupted profiles, and problems with the navigation pane. In such a situation, check if Outlook works on a different device. Then try creating another user account and check if it helps. Also, make sure that you’re using the correct server settings. And if Outlook keeps crashing on your phone, clear the browser’s cache to answer why won’t outlook open, remove the Outlook app, and reinstall it.