posted by rfvv .
He keeps himself in good health.
(What is the part of speech of 'in good health'? An adjective phrase or an adverbial phrase? I think we can substitude 'healthy' for 'in good health'? Then, is 'in good health' an adjective phrase?)
Yes, that phrase is an adjective phrase. If it were adverbial, it would be describing "keeps" -- and that makes sense, too, but the phrase is right after "himself" so that is most logical.