The examples I have found for using a LayoutTransformer with windows phone are all from before they split off the Windows Phone Toolkit from the Silverlight Toolkit.
The Windows Phone Toolkit does not have the LayoutTransformer.dll that was referenced.
So the question is, what do you use to do a LayoutTransform now?
Literally, just use the code from the Silverlight toolkit with minor changes.
Here's how to do it for Windows 8 (note: this is from my blog). You can reuse this completely, just change a few namespaces and at one place from 'protected' to 'public' and it builds and works.
Edit: I published a WP8 version on GitHub. Enjoy :)