Fort Phoenix guards the entrance to the Acushnet River harbor shared by Fairhaven and New Bedford. Local Patriots first fortified the point in 1775, recognizing that wharves, vessels, warehouses, and privateering activity made the harbor valuable and vulnerable. The work initially had no enduring name. Its location allowed cannon to challenge ships approaching from Buzzards Bay, while local militia could watch the channel and protect a maritime economy increasingly tied to the revolutionary war effort.

The surrounding waters saw an early naval action on May 14, 1775, when local men recovered vessels taken by the British sloop Falcon. As the war continued, New Bedford became a center for privateers that captured British commerce. Privateering brought supplies and prize money to the American cause but also made the port a target. By 1778 British commanders planned a destructive raid against communities around the Acushnet and against neighboring Martha's Vineyard.

Major General Charles Grey led thousands of British troops into the harbor area on September 5 and 6, 1778. They burned vessels, warehouses, military stores, homes, and businesses in New Bedford. The small garrison at the fort on the Fairhaven side was overwhelmed or forced away, and the attackers destroyed its guns, carriages, barracks, and magazine. The raid inflicted severe economic damage and demonstrated how exposed coastal towns remained even when the main armies operated elsewhere.

The British attempted further destruction in Fairhaven, but militia under Major Israel Fearing rallied and resisted them. Local tradition credited this defense with helping save the village. The fortification was rebuilt after the raid and for a time was called Fort Fearing. In 1784 it received the name Fort Phoenix, invoking the mythical bird reborn from its ashes and turning the memory of destruction into a story of communal recovery.

The site continued to serve military purposes. The fort was repaired or reconstructed in later periods and was armed during the War of 1812. A new powder magazine and eight-gun installation supported harbor defense during the Civil War, and weapons returned during the world wars. These later layers changed the physical fabric, so the surviving earthworks, stonework, and guns should not be assumed to be entirely those seen by the 1778 garrison.

Today Fort Phoenix State Reservation preserves the commanding view that gave the position its value. The marker's concise sequence—built in 1775, destroyed in 1778, rebuilt—captures the origin of the name but only part of the story. The site links privateering, coastal defense, civilian loss, militia resistance, and repeated reuse across generations. Its preservation allows visitors to read both a Revolutionary battlefield and a long history of how a harbor community prepared for danger from the sea.