The given phrase "I'm thirsty" suggests that the person is feeling a strong desire or need for a drink. This could be due to dehydration or simply feeling parched. The other options, "I'm hot, I'm hungry, I'm cold" do not indicate a need for a drink specifically, but rather refer to different physical sensations or states of being. Therefore, "I'm thirsty" is the correct answer as it best fits the given phrases.