Sure! Here's a simple example of an RPG game powered by ChatGPT where you can interact with NPC characters using JavaScript and Phaser:

1. Initialize Phaser:

```javascript
const config = {
  type: Phaser.AUTO,
  width: 800,
  height: 600,
  scene: {
    preload: preload,
    create: create
  }
};

const game = new Phaser.Game(config);
```

2. Preload assets:

```javascript
function preload() {
  this.load.image('player', 'path/to/player.png');
  this.load.image('npc', 'path/to/npc.png');
}
```

3. Create characters and chat functionality:

```javascript
function create() {
  // Create player
  const player = this.physics.add.sprite(400, 300, 'player');

  // Create NPCs
  const npc1 = this.physics.add.sprite(200, 200, 'npc');
  const npc2 = this.physics.add.sprite(600, 400, 'npc');

  // Enable interactions on NPCs
  npc1.setInteractive();
  npc2.setInteractive();

  // Enable physics for player and NPCs
  this.physics.add.collider(player, npc1);
  this.physics.add.collider(player, npc2);

  const chatBox = document.createElement('div');
  chatBox.style.position = 'absolute';
  chatBox.style.bottom = '0';
  chatBox.style.padding = '10px';
  chatBox.style.width = '100%';
  document.body.appendChild(chatBox);

  npc1.on('pointerdown', () => {
    const message = 'Hello! How can I help you?'; // Send player's message to ChatGPT to generate NPC's response
    const npcResponse = 'Response from ChatGPT'; // Replace with actual response from ChatGPT
    displayMessage(message, npcResponse);
  });

  npc2.on('pointerdown', () => {
    const message = 'Hi! What do you want to know?'; // Send player's message to ChatGPT to generate NPC's response
    const npcResponse = 'Response from ChatGPT'; // Replace with actual response from ChatGPT
    displayMessage(message, npcResponse);
  });

  function displayMessage(playerMessage, npcMessage) {
    const message = document.createElement('p');
    message.textContent = 'Player: ' + playerMessage;
    chatBox.appendChild(message);

    const response = document.createElement('p');
    response.textContent = 'NPC: ' + npcMessage;
    chatBox.appendChild(response);
  }
}
```

Replace `path/to/player.png` and `path/to/npc.png` with the actual paths to your sprite images.

Note: This example demonstrates the basic structure of an RPG game with NPC characters. You need to implement the ChatGPT integration separately to generate NPC responses based on the player's input.

Make sure you have Phaser installed to run this code. You can install it using npm: `npm install phaser`.