Why my g3 has high temp?

I also have a G3. I believe the temperature comes from the processors trying to serve the screen. Since its 2k it takes quite a bit of power. My phone also heats up under medium-low load.

I would suggest taking off the back and checking the battery isnt bulged.

This is common for the lgg3 to be hot. the prossesor has virtually no cooling and with the 1440p screen, it will heat up quite a bit, my solution is to not watch videos at 1440p, enable eco mode so it consumes less power and if youre an expert with tech, open it up and add thermal pads and graphite, you can watch on youtube how to do that. that should decrease the temps a bit