Answer:
The next day
Step-by-step explanation:
The term coherence comes from the Latin word meaning to stick together. A coherent text is a text that consists of well-connected words, sentences, and paragraphs. Every sentence and paragraph should contribute to the meaning of the text as a whole, and be properly linked. Coherent texts are easy to read and understand, with a good and smooth flow.
The phrase that significantly contributes to the coherence of the given passage is The next day. Without it, the sentence We took the test and I think I did really well and the following sentences wouldn't seem as connected to the previous part of the passage, and the text wouldn't be as coherent as it should be.