• I put my phone in my front pocket, instead of the back, so I'm not sitting on it;
• I then make sure to buy pants with front pockets deep enough that my phone is not being pressed into my groin when I sit;
• and I take my phone out of my pocket if someone is about to sit on [or straddle] my lap, charge into me at waist height, or drop a large object on my leg while I'm laying on my side.
You know, common sense.