All lightning wallets are ultimately hot wallets. In my humble opinion, you should only have in any hot wallet money you are willing to lose. So no if you need something that is highly secure for 5 years+, I would say it is not safe enough. There is a lot of nuance and degrees of safety, but to just simplify it hot wallets should be money you are willing to lose.

Phoenix is amazing so most likely nothing will happen, but any lightning wallet has risks. They are often hard to understand, predict, and quantify.