The reason for this is that while all the individual electronic components, the PCB, and even likely the peripherals such as the display panel, are all very lik

The reason for this is that while all the individual electronic components, the PCB, and even likely the peripherals such as the display panel, are all very likely rated for at least 70-85C, the lack of active cooling in smartphones is why an ambient temperature of >35C would spell disaster for smartphones (fortunately due to temperature awareness of the SoC, the SoC just shuts off). Even though the smartphone SoCs may dissipate around <2W of heat, to transfer that heat out of the chassis is pretty hard. This is coming from experience from working on a consumer electronics product where we have run at least 20 heat simulations on Autodesk and learnt how tough it is to dissipate out even 0.75W heat.