Please note that, for most older homes that use a router to provide access to the internet, the signals are sent through a copper cable. The copper cable came first, providing analogue signals for a (landline) phone. With the growth and availability of the internet, the copper cable was also used to provide broadband digital signals at higher frequencies which are terminated on a router.
Now digital voice is prevalent, the old analogue voice network is cumbersome and has disadvantages. The analogue voice network will be switched off in 2025 but digital voice has been delivered over the internet for many years and this will carry on. For those using the old, analogue phones (these are the landline phones), the digital voice signals will need to be amended for landline phones using a converter. I believe that the provider will be offering that service as part of the switch over. Analogue phones require a small electrical current to be delivered to them, also along the copper cable - it allows for emergency calls. Removing this capability has implications for analogue phones so a battery back-up provision is likely too. However, although the analogue voice service is to be switched off, there will be provision for those who prefer 'landline' services. You won't be forced to use mobile phones.
Copper cable has been superseded by optic fibre and this is being rolled out at speed and can be terminated in the house, depending on build and difficulties in connections. If you are using optic fibre, cable TV (with internet connection), or in rare cases satellite to make your phone calls, you probably don't have a landline. Otherwise you have a cable into your house that is capable of providing landline services. Some use landline services and some don't but a copper cable into your premises means that you are capable of getting landline services, even if you don't know it.