PHP_INT_SIZE returns 4 But my Operating System Is 64 bit

Integer size are always compiler/interpreter/platform dependent (this applies for other languages too).
In the case of PHP on Windows it does not support 64-bit integers at all, even if both the hardware and PHP are 64-bit

On windows x86_64, PHP_INT_MAX is 2147483647. This is because in the underlying c-code, a long is 32 bit.

Linux on x86_64 uses a 64bit long so PHP_INT_MAX is going to be 9223372036854775807.

If you need a bigger precision you could use either GMP or BCMath extension.

Tip: never make assumptions on the max value a type will be able to handle unless you need exactly on which php version/platform the code will run.