It is going to happen in December 2025 so you have plenty of time to prepare.
Landlines are moving from analogue to digital, as this article explains.
You should not need to do anything unless you have a very old phone.
I am with Vodafone and the switch has already happened for me. I didn't like the sound quality when using my not too old phone so I got a new VOIP one for only a few pounds. Most of us will not notice any difference except that the phone will be plugged in to your broadband router instead of the wall phone socket.
Just a heads-up for those who missed the info.