The whole point of a burner is that you don’t trust it. You only store what you absolutely need to store on there, if anything, and basically assume it’s compromised the second it leaves your sight.
The advantage of a burner phone is that it can’t contain anything important, because you’ve never put anything important on it, or connected it to any system that contains important data. So it doesn’t really matter if it’s compromised, because the whole point of a burner, is that it’s so unimportant you can burn it the moment it so much as looks at you funny.
Something a lot of people don't really consider is that people who are doing things that could get them unwanted attention, they wouldn't have incriminating evidence on any device, burner or otherwise. So the theoretical ways around not getting busted, like using a burner, are for movie villains and bond type secret agents. Real criminals (smart ones anyway) aren't conducting anything important over any network, be it ip, telephony, morse code, smoke signal, or otherwise, regardless of the burn-ability of the device they would be using to do so
That’s why I chose a low end mass market smartphone as my example.
My wife works for the government in a low level role that involves some amount of travel to local authorities (other major areas in Scotland). She has a phone, and strict instructions to never carry it across the border ofmany countries (as a blanket policy). They’re told they’ll be provided a device for travelling and not to install any work apps on it. It’s basic security - don’t travel with information that you can lose control over.
The advantage of a burner phone is that it can’t contain anything important, because you’ve never put anything important on it, or connected it to any system that contains important data. So it doesn’t really matter if it’s compromised, because the whole point of a burner, is that it’s so unimportant you can burn it the moment it so much as looks at you funny.