A phone benchmark and a phone game session measure different things. The gap between them is thermal, and it determines what mobile developers can actually rely on.
A phone has almost no way to shed heat
There is no fan, very little internal volume and no meaningful airflow, so heat leaves mainly by conducting through the frame and radiating from the surface.
That path is slow and limited, and it gets slower when the device is held in a hand or placed in a case, both of which are normal conditions.
The chip can therefore produce far more heat than the body can remove, and the imbalance appears within a few minutes of sustained load.
Throttling is the designed response
Firmware monitors temperature and reduces clock speeds as limits approach, protecting the components and the comfort of the person holding the device.
The reduction can be substantial, and it arrives gradually, which players experience as a frame rate that was fine at the start of a match and poor by the end.
Because it is temperature driven, the same phone performs differently indoors and outdoors, and a warm room changes results measurably.
Peak numbers describe a state that does not last
Short benchmarks capture the boost period before heat accumulates, so published figures represent a condition a game never operates in.
Developers target the sustained figure instead, which can be a large fraction below the peak, and they verify it by running the game for an extended period rather than a short one.
This is why a phone that scores well can still deliver a worse gaming experience than one with a lower score and a better thermal design.
Charging makes everything harder
Fast charging generates its own heat inside the device, and playing a demanding game while charging combines two thermal loads in the same enclosure.
Many phones respond by slowing charging, reducing performance, or both, and some display a warning and suspend features entirely.
Long sessions therefore work best on a charged battery rather than a charging one, which is the opposite of what most players assume.
Design responds by lowering the ceiling
Mobile developers commonly cap frame rates, reduce resolution dynamically and simplify effects when temperature rises, which trades peak fidelity for consistency.
A stable lower frame rate feels considerably better than one that starts high and decays, because the decline is far more noticeable than the absolute figure.
Accessory cooling and dedicated gaming handsets exist to move the limit, but for the vast majority of devices the thermal envelope remains the binding constraint.