慢腾腾 is an expressive state adjective (状态形容词) built with the reduplicated suffix 腾腾, which adds a vivid, unhurried feel. It describes the manner of moving, speaking, or acting in a slow, leisurely — sometimes annoyingly sluggish — way. While the POS label says verbal phrase (v.p.), the word actually functions as a predicate or complement, like an adjective, and is most natural in the pattern 慢腾腾的 + (verb) or as a stand-alone predicate: 他走路慢腾腾的.