Check the small print on your charger if you aren't sure. All you need is a plug adapter so that your charger plug fits. Plenty of travel plug socket adapters on Amazon, and they are cheap. The island uses British style sockets, or class G (two flat horizontal slots below and one flat vertical slot at the top).

Charging an iPhone in St. Lucia is relatively straightforward but depends on your point of origin. The island primarily uses Type G electrical outlets, which are the three-pin rectangular plugs common in the United Kingdom. The standard voltage is 240V at a frequency of 50Hz. Since all modern iPhone power bricks are dual-voltage (rated for 100-240V), you do not need a voltage converter; however, you will need a physical Type G travel adapter to fit your plug into the wall. If you are traveling from the US or Canada, your standard two-pin plug will not fit without this adapter. Many modern resorts in St. Lucia have integrated USB ports in the bedside lamps or wall sockets, allowing you to plug your Lightning or USB-C cable directly into the wall without a brick. It is worth noting that some older hotels may still have a mix of Type G and the American-style Type A/B sockets, but the British Type G remains the official standard for the island's infrastructure.