What is the ruling on swallowing phlegm – may Allah honor you – during prayer?

Phlegm is pure, not impure. This is based on the prophetic tradition where the Prophet, peace and blessings be upon him, commanded to wipe away sputum (nukhamah) with a garment or underfoot. Had it been impure, he would not have ordered that. Furthermore, phlegm does not invalidate the prayer if a worshipper swallows it, because it is not food or drink, nor does it carry their meaning. Nevertheless, it is preferable to expel phlegm into a tissue or similar and not to swallow it, because it is considered repulsive.