phase change vs natural action

phase change and natural action both are nouns.

Word	Noun	Adjective	Verb	Adverb
phase change	Yes	No	No	No
natural action	Yes	No	No	No

As nouns, natural action is a hypernym of phase change; that is, natural action is a word with a broader meaning than phase change:

phase change: a change from one state (solid or liquid or gas) to another without a change in chemical composition
natural action: a process existing in or produced by nature (rather than by the intent of human beings)

Other hypernyms of phase change include action, activity, natural process.

phase change (noun)	natural action (noun)
a change from one state (solid or liquid or gas) to another without a change in chemical composition	a process existing in or produced by nature (rather than by the intent of human beings)