I had no idea what you were talking about, but looking it up it does look like it's possible to use phone numbers in navigation systems, primarily numbers of businesses. I was able to find several accounts of the feature using the keywords カーナビ 電話番号検索 - using just ナビ gets a lot of hits for directories of phone numbers (mainly used for identifying spam callers), and using GPS instead of ナビ gets hits for tracking cell phones.

I have never used this and didn't realize it was possible, but I don't drive and rarely take taxis. I can see why this would be popular, especially with tourists - the language isn't a barrier to conveying a number. It also avoids issues with address formatting.