Final answer:
The correct phrase that best completes the sentence is 'Es necesario que' (It's necessary that).
Step-by-step explanation:
The correct phrase that best completes the sentence 'hagas una lista con todos los gastos del mes' is Es necesario que (It's necessary that). This phrase indicates that it is necessary or important to make a list of all the expenses for the month. It emphasizes the importance or obligation to complete the action.
Learn more about Completing a sentence in Spanish