When exporting a Revit model to Navisworks, the default settings do not export the phase properties.
You have to change some setting to enable this to happen:
From Revit Application Menu > Export > NWC > Navisworks Settings.
On the File Readers > Revit list, ensure “Convert element properties is checked”
You may want to Convert element Ids, and All element parameters as well (this will give you all the Revit element information in Navisworks but might be information overload)
The resulting NWC file will show the phase information on the selection tree