Optimal Cell Phone Placement

I have a 2012 Prius C. I bought this on Amazon:

Mpow Car Phone Mount, Dashboard Windshield Car Phone Holder with Long Arm, Strong Sticky Gel Suction Cup, Anti-Shake Stabilizer Compatible iPhone 12 11 pro/11 pro max/XS/XR/X/8/7,Galaxy, Moto and More

You can place it as you want - but I have it snaked around the right side of the radio. I don't have the large display that I see yours has. You may be able to figure out a way to place it.

 

I'm using a holder that sticks in the CD slot, which also works for the standard size Gen 3 Prius.

 

I am also using a phone holder that fits in the CD slot and I find it works great for navigation

 

"Optimal" probably would be on the dash, about the middle of the windshield.
But that isn't a good place because it might block your view.

We haven't had any trouble with phones located anywhere inside the car........most often sitting in the cup holder.
Try it and see.

 

I guess I didn't fully answer the OP. "Optimal" to me is as high as possible without obstructing any portion of the windshield or dashboard display. Mine does block a portion of the console display and a center vent, neither of which is a concern to me.
There are some dash-mounted ones that would likely work fine, but I didn't want to permanently fix something to my dash though.
I suspect you could also do a suction-mounted one to the tiny window on the side. Those seemed more expensive and more likely to fail over time as the cup is exposed to UV and temp extremes.
Almost all cupholder ones I've seen require you to look down too far. That would certainly be true in the c unless the holder had a really long "neck". It's not as bad in the Gen 3. We also use the cupholders so it's not an option I've considered anyway.
I'm not sure how true vent-mounted ones remain stable. The one from Proclip isn't attaching to the actual vents. It is likely the best overall mount, but you pay a high price for it, too. Thus, I went with the CD option.

 

Well yes BUT he specified "for navigation".
In my opinion, the ONLY safe way to use a nav application is with voice prompts only.
I never look at the screen while moving; well almost never.

 

I have mine mounted directly behind the steering wheel where the speedo would be in most cars. Means whatever navigation I have can be looked at with a quick glance.

 

Here's mine. And I can still move the vent slightly up and down. Don't have to take my eyes off the road and easy reach.