Sure, here's an example of a simple FPS shooter game implemented as a single HTML file using JavaScript. Please note that this is a basic example and can be further expanded and improved upon.
To play the game, simply open the HTML file in a web browser on your smartphone. You can use the arrow keys or virtual arrow buttons on your smartphone's keyboard (if available) to move the player character around the screen. The player character is represented by a red square on the canvas.