I don't have a separate phone for cryptocurrency stuff by the reason that I have no other interests besides crypto and therefore employed the only phone I have for these purposes. Just kidding. If I had to use a specific device just for crypto I would consider installing special privacy-preserving, de-googled operating systems like CalyxOS, LineageOS, GrapheneOS, Copperhead, etc. With these, I believe it is much easier to reduce the attack surface, safeguard your wallets and keys and, which is also important, reduce the possibility of being tracked by installed apps, google, your ISP, and even the government. Everything, in this case, is open-source, verifiable, secure, and decentralized, essentially follows the basic principles and ideas embedded in bitcoin.
I fully support you. I have a separate laptop that I open only when there is a need to work with cryptocurrencies. And I also don’t trust Windows systems, neither. I prefer Linux systems that are open source, and accordingly, the programs that I need are open source.
As for mobile phones, I don't trust them at all. Android is famous for its pirated applications, which are already installed in the pre-installation.
And iPhones are simply an open window for manufacturers since they spy in such a way that the user, even with the Internet turned off, manages to send them his data. Accordingly, I use the phone only for its intended purpose.