More details on Microsoft’s multifaceted bet-the-company strategy on Windows 8; check the full article for more perspectives from Paul Thurrott
Windows Phone 8, codenamed Apollo, will be based on the Windows 8 kernel and not on Windows CE as are current versions. This will not impact app compatibility: Microsoft expects to have over 100,000 Windows Phone 7.5-compatible apps available by the time WP8 launches, and they will all work fine on this new OS.
Windows Phone 8, as its name suggests, will also be tied closely to the desktop version of Windows 8 in other ways. They'll be launched closely to each other, and will share integrated ecosystems, thanks to the shared underlying code, components, and user experiences. Windows Phone 8 is part of the "Windows Reimagined" campaign that Microsoft announced for Windows 8. This makes sense as they're companion products in every sense of the word.