I'm wondering what the advantages/benefits are of a dedicated device and if I should get one for the bike.
If you are in a city and don't drive out someplace without cell signal a Phone may be just fine.. Myself.. I have a lot of dead spots in my area and a GPS is a better option. I have no idea if they have phones with SAT GPS built in when cell service goes out... I assume they do for a cost or the better phones.. dunno.. I use a phone as a phone.. Anyways..
Unfortunately, unless you spend 400.00USD or better for a motorcycle GPS, you might find it hard to get navigation voice to a bluetooth headset..least that is what I find.. I updated an old Garmin for the truck to a garmin 51 with free map updates and bluetooth thinking it would work with Automotive bluetooth for speakers etc.. it does not (for me).. nor does it pair with my cheap helmet bluetooth device.. which I figured it wouldn't after the Automotive experience.. The ones designed for an auto for all I can tell, just use an app on the phone for traffic alerts in real time for the bluetooth..
Then there is the rain/water issue.. using a Automotive GPS means using a case to surround it..which gets kinda big but works.. you can view the map for info but you will not get the voice alerts for turns in the helmet (at least I can't).. but it works out.. with a grand total of say 150.00 (GPS,mount,case) if you buy refurbished.. which to "me" is as good s new.. my "opinion"..
Garmin and tomtom both offer good Motorcycle only GPS which will get that voice navigation to a helmet and also be water proof and glare resistant..
Just my thoughts on this... hope it helps..
All that said.. Google Maps on your phone can get it done with downloading directions before you set out on your trip.. and u get the sound in your helmet... boils down to want.. The GPS to "me" gives a nice layout with your speed and posted speed limit etc etc and a clear good size picture.. so depends on the size of your phone I guess.. or..you can watch it on the good screen of the GPS and still run Google maps along side to get the audio commands in the helmet.. they should sync/time together right? lol, I may have just solved my own problem..
How a Phone GPS works:
https://stackoverflow.com/questions/33637/how-does-gps-in-a-mobile-phone-work-exactly#33707