Some phone directories were said to include made up names and numbers that could be used to copyright phone directories. i.e. Company A provides a phone directory with a smattering of nonsense data contained within, Company B copies that wholesale which gives Company A ammunition in a copyright case as they point to the nonsense data and ask Company B to explain why they are included (which they obviously can't without saying, "We copied your directory"). This may just be urban lore.

It is definitely true as to maps; terrestrial maps include streets that don't actually exist. (Nautical maps don't do this.)

I haven't heard of it for phone books, but it could be true.