My opinion is that a dedicated vehicle GPS is much better than a phone. I'll use my phone when I need to, but the dedicated unit provides much more. Pictures of complicated exits and indications of which lane you need to be in before you get there are a big deal to me.
I've been helping a Luddite friend's wife learn their Garmin RV 760LMT. It has the typical weight and height information for an RV unit, but one thing that has sold me on it is the ability to plan a route and then upload it to the unit for use on the road. I can see that being a big advantage when you want to apply some brain power to choosing the best route and still have the GPS give you turn by turn guidance.