Safe Dash Adhesive

I don't know if you're committed to using adhesive or tape, but I had good luck with a ProClipUSA cell phone holder. They are built to clip to specific points on your dash. The positive is they are very sturdy and don't cause damage(in my experience). The negative is they only work in the one spot they are designed for(and they're a little spendy - approx $75-$175).

For a 2018 Prime, the mount location depends on which infotainment screen you have. The one for the smaller screen mounts on the HVAC vents above the screen. The one for the bigger, portrait screen mounts to the dash on the right side of the screen; honestly not the best location, but apparently there weren't any better choices.

If you get one, they come with little bits of double sided tape preinstalled if you want to affix them "permanently". I wanted the option to remove it easily, so I left the tape on to act as a cushion, but I never removed the cover film to expose the adhesive.

Here are the two options for the 2018 Prime:
https://www.proclipusa.com/products/855311-proclip-angle-mount-toyota-prius-2017-20xx
https://www.proclipusa.com/products/855200-proclip-center-mount-toyota-prius-2016-2018

Once you choose the base, you then you chose whatever size device holder you need and whether or not you want some form of charging added to the holder. That accounts for the variance of the price above.