The best defence is to keep the device offline and make sure it only contains the necessary app (The mobile wallet). Perhaps keep it somewhere like in a vault and not move with it every day like how you would do when with a normal mobile phone.
To keep the device offline, the device is only made for wallet or backup only, not for use in other activities.
But the possibility of death and damage will definitely exist. don't expect too much from storage that uses a smartphone.
Better buy and use a secure hardware wallet.
Apparently, there are USB cables that look like normal mobile phone chargers that can plant spyware/malware into your device if you connect them to your device even just once.
So be careful with any USB that is not yours. Don't use USB cables carelessly.
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Believe me, you should have known better than any other. Electrum is what you have been looking for unless you have some money to spare on buying a hardware wallet.
Create a new wallet with Electrum then transfer all your assets to it. If your wallet's ssed/wallet file is safe enough then all your assets are safe.
Electrum is the best Open-source Bitcoin wallet, and I use it for my Android and computer, But Phrase security is the responsibility of the user.
Make sure all devices are safe from malware.
If you want to be more secure, you should use a Hardware wallet.
It's very affordable, and even cheaper than the assets you hold.
But choose a hardware wallet that has good security and does not provide phrase recovery because it is dangerous,
like the current trending one (ledger) which will be updated with a 24-word phrase recovery system LOL.