Just buy a real GPS.
It's about ease of use. To flag a waypoint along a route ... I don't even know how to do that on my phone, it takes so many menu, press-and-hold, click this, drag that operations. With my GPS, "Mark" button, "Enter" button to save the point. Don't even have to look at it.
The few times I've been in my truck and left my GPS at home, trying to find and navigate to an address takes for-fucking-ever on the phone. GPS is a little more difficult for data-entry, but a lot more forgiving than the tiny-ass touch screen keys on the phone. And the GPS doesn't try and auto-correct street or city names.
Right tool for the job n' shit.