The antonyms for the phrase "most well kept" are "messy," "dirty," "grimy," "neglected," "unkempt," and "slovenly." These words reflect the opposite meaning of the phrase, which suggests that something is in good condition, neat, and organized. A place or object that is described as "messy" implies disorderliness and untidiness, possibly indicating a lack of care or attention. Similarly, the term "dirty" indicates the presence of dirt or filth, while "grimy" suggests that something is covered in a layer of dirt or grease.