I stumble upon an excellent icon alternative made by Bernard Kowalski to the boring standard PhpStorm icon. You can download it here 😉

Here are the steps to replace your PhpStorm icon so it shows within the application itself:

1. Right-click on PhpStorm.app and Show Package Contents
2. Navigate to Contents/Resources/
3. Replace webide.icns with custom icon (making sure the name is exactly the same)

Enjoy!