why my phone heat during i am using unity 3d apps
to answer your question, the part of why my phone heat, the answer would be → every proccessing machine has a heat production and a heat dissipation, being heat production generated by calculations and their electrical ressistance while performing its actions, and heat dissipation related to materials of the device, ventilation and environment.
as for the part of during using unity 3d apps, the answer would be → 3d apps are high demanding software, the amount of calculations is high depending of the quality of their assets, bad code, and extensive(bad) memory usage, a good way to do this is to reduce triangle count of your gameobjects, reduce the amount of resources loaded per scene, a good memory usage(do not create more variables than you need, do not assign heavy information to a variable if it will not be used, and destroy them if they are not going to be used anymore), optimize code for less line count usually means a good logic algorithm, which means less processing, any best practices for mobile applications could help in this matter, optimization and quality are some good fields of IT so be ready to get your hands dirty to clean those apps, good luck