You may notice that by default when you export to CAD in Revit 2012, the phase status is not included.
For example, in Revit 2011 if the Phase Created of a wall is set to Existing, when you export to CAD it is placed on the A-WALL-EXST layer. Export the same existing wall in Revit 2012 and you notice the wall geometry is placed on the A-WALL layer.
In Revit 2012 you can modify the export setup, and include the phase modifier by doing the following:
R > Export > Options > Export Setups DWG/DXF > Add/Edit Modifiers for All… > add {Phase Status} > OK > OK
Now when you export to CAD the phase status will be included, in this case A-WALL-EXST:
You can save multiple export setups in Revit 2012; I have included some WikiHelp documentation below:

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Hi Ryan
I Just can't figure out how to save my layer mapping to txt in 2012. Is that not an option anymore?
\Peter
Posted by: Peter Tranberg | July 22, 2011 at 08:18 AM
Peter Tranberg
You can Only Save it as a Template or Project File then take it using 'Transfer Project Standards'
Posted by: Mahmoud Abdelmoneam | August 25, 2011 at 08:53 AM