Now I am being a little concerned here because I have my coins stored on a smartphone wallet.
But I am using Mycelium which is an opensource wallet for storing bitcoin and Exodus for altcoins which is partiall open source.
At the same time the phone is completely separate and has no other apps installed. I don't use it for anything at all.
i wouldnt store any significant amount on a phone.
that being said ive used mycelium for years on my daily driver android phones that are on 24/7 (and that are always fully patched and running the latest OS that are supported) and never had a problem, but its just very small amounts and im fully prepared to lose them at any time due to whatever reason (hacks/stolen/wallet goes bad/whatever).
hardware wallets for the win. paper is good but only use them if you know what youre doing.