Although Skype for Business will remain alive and well on the iOS and Android handsets, as well as on Mac and Windows desktops, Microsoft decided to stop supporting it on Windows Phone. In addition to it, Microsoft Teams and Yammer for Windows-driven handsets will no longer be supported starting next month as well.
https://www.notebookcheck.net/No-more-support-for-Microsoft-Teams-Yammer-and-Skype-for-Business-on-Windows-Phone-starting-next-month.300760.0.html