Probably an old copper line. The phone companies do not properly maintain them anymore.
Up until i retired in 2019, we used POTS (Copper wire, plain old telephone service) as our redundant, back up service in the hospital. We had “direct” lines to every floor. Our main service was all Voice over IP, and it was located in Ohio…while we were in MA.
One day a back hoe outside of the facility in Ohio dug up a fiber. We lost most of our telephone service in New England.
There was hell to pay for that! Putting all of your eggs into a “cheap” basket can bite you in the rear end.
Sometimes the old way is the most reliable.