Once the phone is on, they can tie it to a person with geolocation. Either directly if you do it at home, or indirectly when traveling in a vehicle associated with you.
This is advice for a world that doesn’t exist any more and hasn’t for a long time. The only thing you are going to do following this advice is to stand out immediately amongst a sea of data that you are someone who is taking very unusual security measures and worthy of a closer look. It’s a very easy to identify signature and it’s very literally the opposite of what you should be doing in 2025.
The countries I am familiar with in Europe (NL to name one) you can buy sim cards without any ID. Additionally there's at least 1 provider I know of that's giving them away for free while for the majority you pay 1-5 EUR but get some data after activation.
There's no limit on how many you can purchase at once either.
In Estonia, you could buy a prepaid SIM card in a convenience shop a few years ago, without any sort of ID verification. Not sure if that’s still an option but I think it’s not a priority there. You can then use it all over the EU.
And of course, buying a phone without a contract doesn’t require ID either.