The point isn't to have or not to have a mobile device. The point is the ecosystem of Android and Apple devices that give two manufacturers close to monopolistic power on data access and use. Which is kind of the opposite of the principle of digital sovereignty.
Also: I said "modern enough" for a reason. Some solutions need a feature that only the newer/newest generation of mobile devices offers (NFC, Secure Enclave, encrypted storage, Bluetooth > 4.x etc).
