I don't think this story is fully understood. Openreach will phase out the copper PSTN network and ISDN in 2025. The associated products they sell wholesale to service providers based on these technologies will cease. BT as a service provider (as opposed to Openreach) will stop supplying any form of traditional phone line to businesses (but not home users) at the same time. Other providers will probably follow suit, but don't have to.
That's not quite the same as phasing out normal phones entirely. The last bit of copper going into buildings will remain and any domestic services currently used (including a landline service) will continue, it will just be data based behind the scenes with equipment in the cabinet to convert. It does mean the default will likely be to sell 'naked' DSL/FTTC products which don't include a phone number and line and consequently there will probably be a drastic reduction in the number of landlines in use, but it will still be something you can specify if you want. Openreach will also offer a 500Kbps 'Virtual Analogue' wholesale product specifically so service providers can continue to provide a traditional style phone line compatible with analogue PSTN equipment to people who just want a landline with no internet. Customers on those products will continue to just plug in a phone and it will just work.