If you buy a phone with cash or Bitcoin & then use it with your phone service, &/or home internet...
You can't be sure that phone isn't now connected to your identity.
Discussion
If you don't need this level of privacy you can buy a new pixel straight from Google,
This doesn't change the use case of Graphene or Calyx - you should still execute your way to max security.
Yeah if you really need a phone that's not tied to your identity **at all** taking it to your home is probably the stupidest thing you can do. especially if you already have a phone that's attached your identaty at home.
best practice is to get a feraday pouch and put your phone in that pouch a significant distance from your home and don't take it out unless you far enough away from home. and leave your daily driver at home when useing this phone.