What are you hoping to achieve by sanding your chrome mate? Remove it? It certainly won't do it any good, but isn't a good idea, if you want to remove it, take it to a chrome platers and have them remove it, then you'll have nice clean rims to paint or powdercoat, or to re-chrome.
Phosphoric acid is great for removing rust from chrome, if you just want to clean it, but don't get it on your spokes as it'll remove the zinc plating very quickly. Whatever you choose to do, use "Wet and Dry" sandpaper wet, for the best results. Cheers, Terry.