Okay, the user wants a top-down alien shooter using Phaser with procedurally generated graphics. Let me start by recalling how Phaser works. I need to set up a basic game structure with a scene, handle player movement with WASD, create enemies that move towards the player, implement shooting mechanics, track health and score, and increase difficulty over time.

First, I'll need to create the HTML file with the Phaser script included. Since the user specified to use only the provided phaser.min.js, I'll make sure to reference it correctly. The HTML will have a canvas element where the game runs.

Next, the JavaScript part. I'll start by defining the game configuration, setting the type to Phaser.AUTO, and specifying the width and height. The scene will include preload, create, and update functions. But wait, the user wants procedural graphics, so I can't use images. I'll have to generate sprites using Phaser's graphics API.

For the player, I'll create a circle using the Graphics class, maybe with a fill style. Then, handle input for movement. The WASD keys will control the player's position. I'll need to update the player's position in the update loop.

Enemies need to be procedurally generated. Maybe create them as circles with random colors. They should move towards the player. I can use a simple vector calculation for their movement direction. Also, waves of enemies: perhaps spawn them at intervals, increasing the number or speed over time.

Shooting mechanics: when the user clicks or presses a key (like space), create a projectile. The projectile should move in the direction the player is facing. Since it's top-down, maybe the direction is based on the mouse position or a fixed direction. Wait, the user didn't mention mouse aiming, just aiming and firing. Maybe the player can aim by moving the mouse, but since it's top-down, perhaps the shooting direction is fixed or based on the mouse position relative to the player. Hmm, the user said "aim and fire", so maybe the direction is determined by where the mouse is. So I'll need to track the mouse position and calculate the direction vector from the player to the mouse.

For collisions, when a projectile hits an enemy, both should be destroyed, and the score increases. Enemies that reach the player's position will decrease health. Health and score need to be displayed on the screen, maybe using text objects.

Difficulty increase: as waves progress, enemies could spawn faster, move faster, or have more health. Maybe after each wave, increase the enemy speed or the number of enemies per wave.

Procedural graphics: all sprites (player, enemies, projectiles) are created with Phaser's Graphics class. For example, the player is a circle, enemies are different colored circles, projectiles are small circles.

Testing the code structure: the scene's create function will set up the player, enemies, projectiles, and UI elements. The update function handles movement, shooting, collision detection, and enemy movement.

Potential issues: handling multiple enemies, ensuring projectiles are properly destroyed after hitting enemies or going off-screen. Also, managing waves and difficulty progression.

Now, putting it all together in the index.html file. The script tag will include the Phaser library and then the game code. Since it's all in one file, I'll write the JavaScript inline within the HTML.

I'll need to define the game variables, like player, enemies, projectiles, score, health, etc. The game loop will handle updating positions, checking for collisions, and spawning new enemies over time.

For procedural generation, using random colors for enemies and maybe varying their sizes. The player's sprite is a simple shape, and projectiles are small circles moving in a direction.

I should also add a game over condition when health reaches zero, and display the final score.

Let me outline the code structure step by step, making sure all elements are included and that the procedural graphics are used throughout.

Okay, I need to check if the user's request was fully addressed. They wanted a top-down alien shooter using Phaser with procedural graphics, no external assets. The provided code creates an HTML file with Phaser, sets up the game loop, player movement with WASD, shooting mechanics, enemy waves, health, score, and increasing difficulty.

Let me verify each part. The HTML includes the Phaser script and the game code inline. The player is a green circle, enemies are randomly colored circles, and projectiles are red circles. Movement with WASD is handled in the update function. Shooting is done with the mouse, calculating direction vectors. Enemies move towards the player, and collisions are checked between projectiles and enemies, as well as enemies and the player. Score and health are displayed, and waves increase difficulty by spawning more enemies and increasing their speed. Game over condition is in place, with a restart on spacebar.

Everything seems covered. The code is self-contained, uses only Phaser, and no external resources. The user should be able to run the index.html file and have the game work as specified. No errors in the code structure, and all required elements are present. The answer is complete.