According to charles law when the temperature of a gas at constant pressure is increased it

According Charles law, when the temperature of a gas at constant pressure is increased, the volume of the gas increases.  The law states that for a mixed mass of a gas at constant pressure, the volume is directly proportional to the Kelvin temperature.

That is to say that if for example you double the Kelvin temperature from, say 400K to 600k, at  a constant pressure, the volume of a mixed mass of the gas will double as well.

Charles studied the compressibility of gases nearly 100 years  after  Boyle. In his experiments, he noted that at fixed pressure, the volume of a gas is proportional to the temperature of the gas.