replacement cell phone case

[http://dummy.us.eu.org/robert (Robert)]

https://www.ebay.com/itm/2-NEW-IFROGZ-REAL-WOOD-PHONE-COVER-CASE-CACHE-FOR-GALAXY-S4-ZAGG/282651059212

This one is made of wood.  It may or may not be grippable, 'tho.

https://www.ebay.com/itm/Ballistic-Samsung-Galaxy-S4-MAXX-Series-Case-with-Holster-SX1159-A065-Black/171955167418

This one is made of plastic and rubber, but is rugged and grippable.

https://www.ebay.com/itm/New-Otterbox-Commuter-Series-Case-For-Samsung-Galaxy-S4/283217517120

This one is also rugged and will likely last a while.

The Samsung Galaxy S4 is pretty old, so I couldn't really find any
non-eBay sites which sell cases.