Sure, here is a simple boxing game implemented as a single HTML file with JavaScript:
To play the game on a smartphone, you would open the HTML file in a web browser application and use touch gestures to control the player's movement. The objective of the game is to avoid collision with the enemy by moving the player to the left or right using touch controls. If the player is hit by the enemy, a game over message will be displayed, and the game can be restarted.