Effective May 20, 2018, the Windows Phone apps for Skype for Business, Microsoft Teams, and Yammer will be retired. Starting on that date, these apps will no longer be available for download from Microsoft Store, and Microsoft will no longer support them.
While Microsoft continues to support Windows 10 Mobile, we are not focused on building new features for the system. We will continue to invest in the Skype for Business, Microsoft Teams, and Yammer mobile apps for iOS and Android, and also in desktop apps for Windows and Mac.
I am not surprised Microsoft has been wanting to abandon the windows phone platform for a while they are doing it slowly but surely.