I have been trying to find a way to continue using Microsoft Office Mobile Apps to access Sharepoint 2013 on-premise using Windows Phone 10 and Microsoft has taken the stance that this is discontinued support and that its not a priority for them so not to expect anything soon. If there are any of you that are concerned by this then please leave some additional feedback for Microsoft. You can find the Tech Net article by searching for the following on the Tech Net page. There are some identical posts on several other Microsoft forums that the original author created that you can find on google.
How to access SharePoint from Windows 10 Mobile?
How to access SharePoint from Windows 10 Mobile?