Below is a simple platformer game implemented as a single HTML file using JavaScript. It uses arrow keys for controlling the player on a smartphone. Please note that the game mechanics and visuals are extremely basic for the sake of simplicity.
To play the game on a smartphone, open the HTML file in a browser that supports HTML5 canvas and use the on-screen arrow keys (if available) or the physical arrow keys of your keyboard (if connected) to control the player. The objective of the game is to navigate the player across the platform by jumping and moving left or right. The player's character is represented by a blue rectangle.