I have successfully stored up to 0.3 BTC for 4 years in my smartphone on Electrum wallet. I know this is not the smartest thing to do but I haven't lost my coins because I don't download any app and I don't visit any strange website.
Apart from this being a hot wallet and insecure, you are also storing your coins in a
portable device which is not a good idea because it could be lost, stolen or even damaged (for example if it falls from your hand) and that could lead to loss too.