Using the existing telephone wires is not viable. That has been done in the past but doing so again with current specs and requirements would result in reduced or even sub-standard performance.
If
proper Ethernet cables and connections cannot be installed then you will be wasting time and money.
And remember that it is likely that just relocating the router may improve wireless to acceptable performance levels. Powerline adapters may be an option.
You should not need to gut the house or pull out old cabling.
And what is driving the need for the switch being in the attic? Attic is likely to be hot, cold, etc., and otherwise not good for electronics. Put the switch next to or near the router.
If you own the house you may be able to drill a few strategic holes and run cables through the walls. Will concede that that can be and often is problematic especially with older homes and layouts.
What incoming service do you have from your ISP: coax, DSL, fiber? Make and model modem, router, or modem/router combo?
Do some additional reading and reconsider your plans and options.
For example: the router and switch might be easily moveable/relocatable to another floor between basement and attic.
There are many "how to" articles to be found on the internet. Some good, some not so good.
https://forums.tomshardware.com/threads/want-to-have-ethernet-wiring-in-new-home.3329515/
https://emfacademy.com/installing-hard-wired-internet/
Lots of information here:
https://www.snbforums.com/forums/
Just read and look for ideas. Then plan according to your circumstances and requirements. Post the plan accordingly. You are likely to receive many suggestions and ideas.