A phone can reduce its performance noticeably while still feeling cool in the hand. The control system responds to conditions the user cannot perceive.
Sensors sit next to the heat source
Temperature is measured on the processor package and at several points on the board, close to where heat is generated.
Those readings rise within seconds of a heavy load, long before the heat has spread through the chassis to the outer surface.
The case is the last part to warm, so by the time a phone feels hot the internal limits have usually been active for some time.
Thin bodies cannot store much heat
A phone has very little thermal mass and no fan, so the only routes for heat are conduction through the body and radiation from the surface.
Under sustained load, heat is generated faster than it can leave, and the internal temperature rises until the control system intervenes.
Vapour chambers and graphite sheets spread heat across a larger area, which delays the intervention rather than removing the constraint.
Surface temperature is its own limit
Separate from protecting components, manufacturers cap how warm the exterior may become, because a device held against skin has a comfort and safety ceiling.
This limit is often reached before any component is at risk, and it is why performance can be restricted while the phone is merely warm.
It is also why the same chip sustains far more performance in a tablet or laptop, where the surface area is larger and the ceiling is further away.
Throttling is gradual, not a switch
Rather than a single step down, the system continuously adjusts clock speeds and moves work between high-performance and efficiency cores.
The user experiences this as a gradual decline during long tasks such as gaming, video recording or a large software update.
Benchmarks that run briefly on a cool device never reach this state, which is why sustained testing produces such different results.
Charging and ambient conditions stack
Fast charging generates its own heat inside the device, so charging while playing a demanding game combines two heat sources in a small space.
A warm environment, direct sunlight or an insulating case each raise the starting temperature and shorten the time before limits engage.
Removing a case during heavy use, or charging at a lower rate, addresses more of the problem than any software setting available to the user.