A phone that gets hot while gaming is not broken. It is doing exactly what it was designed to do, and the frame rate you lose is the price of protecting the hardware. Understanding that is the difference between fixing the problem and installing four apps that cannot.

Why heat costs you frames

Phones have no fans and almost no room for a heatsink. The only way to shed heat is through the case and the screen, and that is slow. So when the processor approaches its thermal limit, Android reduces its clock speed on purpose. Less work per second means less heat, and also fewer frames.

This is called thermal throttling, and every phone does it. A flagship simply has more headroom before it starts.

The temperature it starts at

There is no single number across all devices, but most Android phones begin reducing clock speed somewhere between 45 and 50 degrees Celsius at the CPU, and throttle aggressively above roughly 60. If you can see your CPU temperature, that band is the one to watch.

The tell is timing. Throttling produces a characteristic curve: fine for the first ten to fifteen minutes, then a steady decline that does not recover until you stop playing. If your frames are bad from the first second instead, the cause is your graphics settings, not heat.

Ambient temperature matters more than people expect. The same phone and the same game can throttle within eight minutes on a hot afternoon and not at all in an air-conditioned room.

What actually helps

Take the case off while you play. A thick protective case is insulation. This is the single most effective change for most people.
Do not charge while gaming. Charging generates its own heat, right next to the processor, and the two compound.
Cap the frame rate. Asking for 60 fps when your phone can comfortably hold 40 produces more heat and a worse experience than simply targeting 40.
Lower the graphics preset one step. Less GPU work is less heat, and the visual difference during a firefight is negligible.
Keep it out of direct sunlight. Sun on a dark screen heats it fast.
Take breaks. Ten minutes off lets the chip return to its normal operating range.

What does not help

Cleaner apps, RAM boosters, and anything advertising a cooling feature cannot lower your temperature. Software has no mechanism to remove heat from a chip. The most a booster can honestly do is reduce the work being done, by closing background processes, which helps slightly and indirectly.

Apps that display a snowflake animation and claim to have cooled your phone by some number of degrees are showing you an animation. The temperature reading they show afterwards is usually just the sensor value a moment later, which fluctuates on its own.

Cooling accessories

Clip-on phone coolers do work, because unlike software they physically move heat away. A Peltier cooler can keep a phone out of the throttling band for an entire session. Whether that is worth the cost and the bulk is a personal call, but the physics is real in a way that a cooling app is not.

When heat is not the answer

If your phone is cool and the game still lags, look elsewhere. Steady frames with delayed actions point at network latency, and stutter at load points points at memory. The full decision tree is in why does BGMI lag on my phone.