Sure! Here's an example of a simple Pong game for 2 players implemented as a single HTML file:
To play the game on a smartphone, open the HTML file in a mobile browser and you'll be able to control the paddles using touch inputs. The game canvas will be positioned in the center of the screen. The player on the left side can control their paddle by swiping up or down on the left side of the screen, while the player on the right side can control their paddle by swiping up or down on the right side of the screen. The score of each player will be displayed at the top.