Is this an adverb phrase, "You can sleep as freely as you wish." AS FREELY, is it an adverb phrase?

In this sentence: "You can sleep as freely as you want." I think the adverb phrase is AS FREELY modifying sleep because it indicates the time of sleeping. The question would be, WHEN can I sleep? And the answer would be, You can sleep as freely as you want. Is it an adverb phrase? Answer with a YES or NO and if you can provide evidences, enlighten me! :)