I have a lot of the same issues. Bluetooth headset turned up to almost max + foam earplugs works reasonably well, as long as I already have a good idea of where I'm going. Handlebar mounts work fairly well, but putting the phone in the sun in Arizona during the summer often leads to it turning off. There's also quite a few reports of phones either flying off mounts or camera lens/focus dying due to the vibration.

In the end, I normally leave the phone in my pocket, make due with voice alerts, and leave a few minutes early so I can safely miss an exit without panic. The last thing you need on a highway filled with texting drivers (completely legal in AZ) is to be distracted and making multi-lane changes at the last second.