I think the win10 free upgrade has expired

If you do have to phone up to complete activation, your licence permits what you want to do.
Once activated you can "upgrade" to Windows 10, activate online and that licence will be tied to the new hardware for automatic online activation without a product key, should you then choose to do a clean install.
Although the period for free upgrade to Windows 10, from Windows 7/8 officially ended, I've been able to do this since then without any problems (other than giving someone Windows 10).

8 isn't end of life yet so your fine.
Even when it is, MS is pretty good at keeping activation servers going. Vista activated earlier this year, think XP may be broken now though.

Technically Win10 upgrade ended in November 2017 but they haven't really locked it down. If MS ever audit you they can see when the licence was upgraded and asked what entitled you to do this after 2017 although I suspect they are more interested in moving everyone off older versions of windows then enforcing licencing at this point which is why it still works.

Thanks for the answers. I never followed the procedure of phone reactivation and don't really know how it works. Maybe is it possible that the license without being activated after years it already detached itself from the old hardware and available for the new reactivation?
I'll try to install it soon anyway and let you know. 😀

Phone activation is pretty painless, I had to do it for a Win7 machine last month that hardware has changed enough to no longer work online.
It's all automated and thats the 2nd or 3rd time I've done it