"Deep in thought" is a phrase that describes someone who is completely absorbed in their thinking. Some antonyms to this phrase could include "distracted," "unfocused," "uninterested," or "inattentive." These words describe individuals who are not completely engaged in their thoughts, and are easily distracted or interrupted. Another antonym to "deep in thought" could be "superficial," which suggests that someone is thinking only superficially about a topic, without delving deeply into it. All in all, these antonyms suggest the opposite of someone who is lost in thought, and instead depict individuals who are easily pulled away from their thinking or aren't thinking deeply enough.