Chances of your second phone with mobile wallet app being stolen, lost, broken, becomes suddenly a brick after a new firmware update is higher than simply holding funds on a ledger/trezor like hardware wallet.

Imagine your are keeping your phone at home and suddenly someone brakes in. First thing he will steal will be gadgets like phones, laptops - something that will be easy to sell in pawnshop. But who would take cheap usb flash drive, sorry crypto hardware wallet?

Plus this hardware wallets have built in security, and your mobile has? Pin code ? Home screen protection code ?