I insure against things that would be a financial disaster: health insurance, income protection, house insurance, that kind of thing. Having to buy a new phone once in a blue moon is not a financial disaster. It's why I put money into a savings account.
I went for four unscheduled dips in a reservoir earlier this year when the goober I was paired with for the kayak leg of an adventure race managed to capsize us four times in fifteen minutes. My phone was in what I thought was a sealed waterproof bag, but died completely. If I had been paying for phone insurance since 2009, paying about a hundred a year, I would effectively have paid 800 for a refurbished secondhand phone. Instead, I took out half that amount from my savings and bought myself a blazingly fast Oneplus 3T.
Unless you are truly disastrous with smartphones, you're better off self-insuring.