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.
I agree with that. In fact, my old iphone 4 stopped charging some days ago. There I had two factor authentication for some accounts with bitcoin online. Fortunately, I got to change the authentication before the phone died. I would have likely lost access to the coins if I had not realized about the phone not charging.
Not very secure.
Lucky that you managed to spot the charging issue, although i'm sure you could of just repaired the charging module if need be. Also would there not be anything you can store as a backup for those online Bitcoin services and save it elsewhere?