It is possible to identify spot colors in PS. They need to be added each as an individual channel in the Channels panel.
From the Channels panel drop-down menu, select New Spot Channel...
Give the channel a name (ideally, the name of the Pantone color). Click on the color swatch in the same dialog box. In the Color Picker, click on Color Libraries. Select your Pantone color: pick a Book, then quickly type in the color number. Click OK twice.
Paint/fill with black on the channel mask where this color needs to go on your document. You will see your desired color on the screen, and the printer can print each channel as a plate with black on white (ready for inking).
Rinse and repeat with your other spot colors.
Unfortunately, it's not a simple matter of Image > Mode > Spot Colors, or something like that.
