I think there is a default Plot Plan Text Style that you can use or edit to your liking depending on the scale of the plot plan.   Open ALDO ( Active Layer Display Options ) and make sure Layer Properties are turned on.  Select a plot line of the plan and it will show you what layer it is on and what Text Style it is using.  Look for Plot Plan Text Style or hit the define button to make your own.  You will likely need a text height of 30" or more.