A clear phone case might yellow or get dirty eventually, but it's quite simple to clean it. When the case looks dirty, I take it off and use warm water and a bit of dish soap for cleaning it. Then I take an old toothbrush to gently scrub the corners. If some stains don't come off easily, a little baking soda should do the trick. Make sure you rinse it very well and let it air dry thoroughly before installing it on the phone again.