Possibly an item for Whatever Works, maybe the cheapest so far.

Clear Self Adhesive Polyurethane Bumper Stops Feet Bumpons 8mm x 1.6mm Domed (Pack of 50) https://www.amazon.co.uk/dp/B00EXSU7K8/ref=cm_sw_r_cp_apa_o5ifyb412A6DD

I've used them on a Nexus 4 to stop it sliding off the table or charger (and it helped with sound from the rear speaker), my five-port USB chargers to build them in place better. I use them on anything that might scratch a surface or might get scratched.
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