I can't see that this is related to FTTP rollout. There's no way they'll have the whole country on FTTP by 2025, nor will they want to visit every home to install an ONT or VOIP box.
My assumption is that they'll be replacing existing DSLAMs with MSANs, which means you will still be able to plug an analogue phone into the end of your copper line, but it will be digital from the MSAN backwards, rather than the copper carrying on back to the old exchange equipment. This is what LLU providers like Talktalk do already: the line terminates on their MSAN which handles both data *and* voice (turning it into VOIP).
If OpenReach were to take this further then the FTTC VDSL2 equipment inside primary cabinets would be upgraded to MSANs, so they could eliminate all the copper back to the physical exchange. But this would mean getting all wholesale ISPs off of LLU and onto their GEA (FTTC) products.
Maybe they can do this if they make the 40/10 FTTC product so cheap that it's not worth the other ISPs continuing to do LLU. It brings us back round to the days before LLU, where everyone ran on OpenReach's DSLAMs. But we already have that with FTTC and FTTP: no provider can install their own equipment inside a cabinet, nor light up a fibre.