I bought that same product to put into my phone case. But instead of using the included leash I bought this to loop through the case insert, my backpack, and a few of my belt loops. So they'd have to cut some belt loops and both straps off my backpack if they want to steal my phone.

https://www.amazon.com/Approved-Luggage-Lumintrail-Combination-Security/dp/B01M2AHFZ6/