Unless it has been done before, let's gather all the responses we collectively get from asking various services about releasing a Universal App for the Windows 10 platform.
[...]
Thanks for taking the time to send us feedback about the mobile app.
At this time we have no plan to implement a Steam Mobile app for Windows Phone, but we have made updates to make much of Steam now accessible via your mobile web browser.
Please note: using the mobile web browser does not act as a two-factor authenticator for trading.
I'll make sure the mobile team knows that users like you are interested in the app specific features.
https://steamcommunity.com/discussions/forum/8/
If you wish to share an opinion, idea or suggestion, the forums are a great place to do so.