Hate to break it to you, but phone lines have started to be digitized in the early 70s, and by 80, 40+ years ago, your phone call almost definitely passed through an ADC and DAC.
Ausaudio, maybe it was in the USA, but I'm from Russia. Our first digital telephone stations appeared in the 1990s, and then only in large cities. In St. Petersburg (5 million people) back in 2000, some stations did not understand the tone set, that is, they were still relay, purely analog.
But it's not about the dates, of course, but what I wrote, it's true. I had a favorite "audiophile" rotary dial Siemens phone with a carbon microphone, my friend had the same one, so I called him up and evaluated the changes in the liveliness and fullness of the sound of his system on the phone. Of course, it was not possible to evaluate everything, but in general it was clear what was what. Now with digital and even more so with mobile communication, this is simply impossible.