Sure! Here's a sample code for a simple game implemented as a single HTML file using JavaScript. In this game, you control a character represented by a pictogram using smartphone touch controls. Please note that this is a basic example and may not fully resemble a complete game like Roblox, but it should give you an idea of how to get started.
To run the game, you can copy the code above into a new HTML file (let's say `game.html`), and then open the file in a web browser on your smartphone. You should see a game container with a yellow square representing the character. You can then touch and swipe on your smartphone screen to move the character in any of the four directions (up, down, left, right). The character's movement is restricted within the game container boundaries. Feel free to modify and enhance the code according to your game requirements.