i think thermal paste , wont do anything unless you have some kind of heatsink in contact with chips(that’s what oldturkey said above). is impossible in other words.
personally , i am waiting for some thermal pads to arrive (just ordered some), so i can use them between the small gap of the board and the back of my phone (iphone 7 plus)
i am getting so much thermal throttle , even in some light games.antutu report 120.000 points without any modification, if i cool the device with some fresh water on the back or some ice + water on my hand i get 195.000++ points , thats crazy.
i have cleaned the phone from inside , with ultrasonic cleaner filled with isopropyl alchocol (case - board) but still no better results.
i will try to fit those pads (0.2 and 0.3mm thickness) into that phone and i ll report back in some days.