Many countries now assume you have a phone. For example getting UK visa requires a smartphone. I don't think going without a phone is feasible nowadays.

Another question is if going with a burner phone that has just sim card and bank card, sufficient. But then you need appleid/google account on the device, and this again links back to your phone number, and it's not easy in practice to have proper clean device.

Well, assume your phone number is public knowledge.

You can get more than one.

Sure. Assume the one that's attached to your payment is public.

Threat modelling. France is unlikely to tell USA if two numbers are owned by the same person without a good reason.

You can get prepaid ones that you can top up with cash, in many countries you don't have to register them to your name.

> UK visa requires a smartphone

I don't think this is accurate.

she's wrong. i did it on the browser on my desktop. the ui definitely doesn't make it easy to find though.

You can simply use an Apple account for your primary device and a Google account for your burner (or vice versa). Or set up a secondary Apple or Google account. Or use a device/OS that doesn’t require one of these accounts!