Is there any Steam application for WindowsPhone 8? I have seen it for Android and iOS. Please let me know if there's any.
A quick google search (all I searched for was "steam app windows 8 phone") brought me to the Windows Store where there is a Steam app for download. It does work on the Windows 7.5 and Windows 8 platform.
A quick search in the Windows Phone Store will reveal "Steam Center" by DG-InfoTec as the first search result. There are numerous other third-party apps available as well.
If you want an official app, contact Valve.
I'm new here, so can't comment or vote up comments yet, but +1 for off-topic by karancan. Even if asking if an app exists is OK, it doesn't take a lot of effort to search the store yourself before asking.