and phones are extremely hard to made truly air-gap
I keep seeing people telling that phones are hard to airgap and.. sorry, but I'm not convinced.
* one can remove the SIM then mobile internet will no longer be used
* one can turn off NFC (if available); however, not a great attack vector
* one can turn off Bluetooth and go airplane mode; however, not a great attack vector unless 100% targeted
* one can remove/forget all known Wi-Fi SSIDs and set the phone not connect to any other/unprotected SSID
One very good argument is that a burglar will most probably steal that smartphone even if it's older, put a SIM in it and turn everything on, making indeed phones somehow risky for cold storage.
Another very good argument is that somebody in the house would do exactly that too (put a SIM in) because of not knowing it's a "special use" phone.
But all this can easily happen with a laptop too (stealing or plugging in a network cable). And let's not compare online securit between old laptops and old phones because both are bad and also dependent of owner's skills in setting them up.
But if you can't do it you can destroy/damage the SIM card slot in order to avoid someone from your home or a burglar to use it. And if you can't easily access it on your phone, you can just put some glue into it. It is very unlikely that the burglar will manage to fix it on the same day as the thief. So it would leave enough time to transfer your funds elsewhere.
But IMO it's simpler to use a tablet only offering a Wifi connection and to deactivate it in your OS or to physically remove the antenna.
There are maybe some Android GPS with no network connection able to run Electrum app too.