The thing is that phones can be lost, robbed, broken more frequently than a Desktop. It is more a safety thing than a security thing I think.
Exactly this. No matter how safe you coins on your Smartphone are if you just lose your smartphone. Same goes for laptops btw.
That's why I prefer a trusted online wallet.That is so much less secure than either of the two you just mentioned. The most secure is to use a hardware wallet. Having the wallet on a desktop is still very secure, much more so than on a phone and much much more so than an online wallet.