I used one Samsung S4 (about <10h/s) device to calculate if 10 or more can produce a decent amount of profit... and the result was like everyone is saying: it's a waste of time and mobile phones if you're planning to use your own devices because charger's pulling more power than the hashrate.
Those "mobile miners" aren't really designed for "personal" mining but for the so-called "advertisement-substitute" or botnets (hundred or thousand devices that you don't supply power and own will do ).
So @Flyingterlik forget it.
Btw I know it's not "worth" it to mine and that its cheaper to buy (heck even faucets pay more than what I theoretically can mine) but I just love the idea of making old useless phones do something :p
Samsung did a project as a POC a while back, but obviously they have plenty of smartphone resources. If I recall, the things you'd need to do are write a custom firmware for the phone (to remove the powersaving barriers, run 100% util for 24h, etc, all those things phones aren't designed to do), and most importantly hack into the hardware, add a massive external cooler/WB to the chip, and bypass the battery so it doesn't explode. Probs need a custom miner too.
Obviously, once you've done all this you end up with a pretty poor hashrate (compared to a desktop CPU) so really, really, really not worth the hassle. For example, you could go experiment chaining together cheap Ryzens for RandomX, which might actually make some money soon, and would be a hell of a lot easier.