Final answer:
The phrase 'To insure domestic tranquility' is one of the purposes of government stated in the Preamble to the Constitution.
Step-by-step explanation:
The phrase that identifies one of the fundamental purposes of government described in the Preamble to the Constitution is: 'To insure domestic tranquility'. This purpose is directly mentioned in the Preamble and reflects the aim to prevent conflicts within or between the states, thus maintaining peace and order within the nation's borders. It is part of the broader goals of the Constitution which include establishing justice, ensuring peace at home, providing for defense against external threats, promoting the welfare of citizens, and securing the blessings of liberty for all.