I have the new iPhone 7 plus and I bought bully the game and a few minutes in it gets hot but not so hot it burning it gets a bit warm but notiseable heat. However once it’s warm hot it don’t get any hotter but does it kinda stress the phone if I constantly play it ?
I always play and my phone is always hot, I don’t pay attention to it 
I stop playing on my phone when it’s get hot.