Thank you for your replies.
This has been a problem for about 15 years, so it isn't recent. Before now, I was less affected, as I either had my own apartment, was a reclusive teenager, or was young enough that I had a playroom.
I will try a polite interruption the next time this occurs. When I first saw that advice, my reaction was something along the lines of "Don't you think I haven't tried that?". Then I really thought about I realize I hadn't. It had been going on for so long that the ingrained "Don't interrupt me while I am on the phone" rule had long since become habit, and I hadn't dared interrupt her conversation. That post woke me up. And looking at it now it is so obvious, and I feel silly for not having tried it before.