Sure! Here's an example of a single HTML file containing a JavaScript game that meets your requirements:
Tap to Level Up!
In the above code, we have a simple game where you start at level 1 represented by a square. Every time you tap/click on the game area, the level increases by one. When level 15 is reached, the text changes to "Warrior Square".
The game is implemented as a single HTML file enclosed in script tags. It uses JavaScript to handle the logic and updates the game element's content accordingly. The game is designed to be played on a smartphone, utilizing tap/click events. The game visuals are represented by text, but you can easily replace it with pictograms or any other visual representation you prefer.