Connecting your mobile device to email and calendars is one of the first steps after your company completes an Office 365 migration. Many of us use the OWA App on our Andriod or iPhone device. In May 2018 Microsoft will be retiring the OWA or Outlook App on the web mobile application. The process starts in April when they will disable install/download of the app. If you use this application, make the switch to the Outlook App asap. Yes, this is different from the OWA application :(
Below are some conveniences that we will miss…
See a complete list here https://support.office.com/en-us/article/compare-outlook-2016-outlook-on-the-web-and-outlook-for-ios-android-b26a7bf5-0ac7-48ba-97af-984e0645dde5
Information on how to setup the Outlook App for your mobile device