If you want to feel the first hit iPad game known as Osmos game by Hemisphere Games on your iPhone, this app now available for iPhone for $ 2.99. Redesign for iPhone users, you will get many features from Osmos game, including full Retina Display support and Multi-touch awesomeness that allow you to tap to eject mass, pinch to zoom, or flick to warp time.
Osmos for iPhone has two game modes, the Odyssey and the Arcade, where you can get game experiences up to 72 levels. Especially, if you want to play any level types with different difficulty levels, I think you should choose the Arcade game mode. Get more information about Osmos for iPhone here.