A person inexperienced with interpreting phase diagrams would conclude that no water vapour (gas phase) can exist below the boiling point.
Consider the red circle. Temperature is 40C and one atmosphere pressure – a typical day in the Amazon jungle. The phase diagram shows no gas phase, yet we know the humidity in the Amazon jungle is very high. Obviously, the phase diagram does not represent the real world.
Phase diagrams represent perfect equilibrium conditions in a closed system, which never exist on earth. A skillful scientist understands this, yet uses the important information contained in the phase diagram to her/his benefit.
In the Arctic, when temperatures are close to 0C – water exists in all three phases solid/liquid/gas. We are all familiar with this. We don’t have to drop the atmospheric pressure to the boiling point of water at 0C (0.00603 atmosphere) to have water vapour in the air.