..islandhooper:
From what I've not seen, from using search online, is some kind
of 'static-cling' non-adhesive material (thin plastic) with surface
that will adhere to the slippery iPhone; and stay there. (retail)
The "out-side" could contain a micro-abrasive material.
..It could be on a roll, like plastic wrap..
Just a 'pattern of dots' on outside, of piece of Saran®
wrap; held there with a co-hesive simple attraction.
A DIY idea, is not create a case or custom-fitted product.
A few strips of this; to be grippy enough to hang on to.
..Make your own inexpensively by trial-&-error..?
While niche products may cost $$ ~ already exist.
Something cheap & reusable recycled/disposable.
