What is the ruling on swallowing phlegm during prayer, and does it invalidate the prayer? What is the ruling on swallowing a small amount of water remaining in the mouth after drinking during prayer?

Swallowing phlegm invalidates prayer according to the Maliki and Shafi'i schools if it was possible to expel it. However, a small amount of saliva that flows with the spittle does not invalidate prayer if swallowed.