If you look at the way some people carry their smartphones, it's no wonder that the cracked screen industry does a thriving business. To help myself be more cautious, I picture my Pixel 2 as seven, $100 bills (its actual cost to replace) and that I'm walking over grates with large openings ready to swallow my money into a sewer below. Those imaginary grates are sized to roughly represent the probability that I will lose some, and possibly all, seven Benjamin Franklin's if I don't handle them with the care they deserve.
People act more responsibly when using cash and using this technique leverages that fact. Try it and see if you notice a difference in your behaviour.