There's a technique called sim swap, which enables a fraudster to transfer the victim phone number to an other sim, allowing a fraudster hence to read the messages but especially to empty out their bank account by recovering or changing the bank website account password via phone number, so by receiving a recovery code or something like that. Anyway this can be avoided by setting a number unknown to anyone.
The problem is that maybe anyone who has my phone number could potentially use this technique just to associate a Google account or any other account to my number, in order to commit crimes on behalf of my identity. How can this thing be prevented in the first place?
I mean, in this case I could have as many unknown numbers as I want but, a perpetrator can still use this technique with my known number, and even if my acquaintances are not evil minded, they can just give the number to other people who give it to other people as well, until my number happens to be in wrong hands.