Office 365 (Outlook 2013 / 2016 / 2019 for Win) - Change the Appearance of the Navigation Pane
The navigation pane is the bar along the bottom of Outlook that contains the Mail, Calendar, People, and Task options. You can increase the amount of work space in your Outlook window by using the minimized Navigation Pane. The minimized Navigation Pane collapses into a much smaller bar of buttons that still provides access to these options.
1. Click on the three dots in the navigation bar at the bottom and select Navigation Options.
2. Check Compact Navigation and then OK to minimize the pane. To maximize, click on the three dots, select Navigation Options, uncheck the Compact Navigation box, and select OK.
3. While in the Navigation Options window, you can also change the number of items that are visible and change their order.