Why does vomiting phlegm (Balgham) NOT break Wudu, even if it is a mouthful?

Ablution (الوضوء): Invalidators (نواقص الوضوء) Part 1

• Because phlegm is considered pure and not a filth (Najasah) in Hanafi law.
• Because phlegm comes from the pathways.
• Only if the wudu was made with seawater.
• Because the volume of phlegm cannot be measured.