Wallet makes sense in the back pocket. It's been kind of the default for generations so much it's a comedic point in TV Shows and movies at times. They're generally malleable and an easy place to grab, for better or worse.
Phone on the other hand, I don't get either. They're rigid and can break quite easily if sat on. 🤷♂️
Most front pockets on women's pants are too small unless it's the dreaded fake pocket (Curse you cute pair of jeans!). Thus usually in my back pocket while walking and not in use. It is removed when sitting though.
It's uncomfortable to walk up stairs and uphill when my phone is in my front pocket. Plus the movement to get it out from my back pocket is so much swifter.