Turns out it's been there at least a few years and I just hadn't noticed it earlier - or forgotten about it.
But why is it still there in 2020? I'm speculating: It may be because of the store's proximity to a road junction where in the past people would often be waiting for a ride to a another small community. I suspect cell phones were a rare item in that group. I'd sometimes see people there late at night, and can imagine them wandering to the store and asking to use the phone to call for a ride. That would be irritating if it was a regular occurrence. There's now a free bus service between the communities, and I haven't noticed anyone waiting there since it started. I wonder if the phone gets any use these days. I'm now curious to when it will disappear as all the others have.