I'm not sure if your "Physick" icon is under the listed icons you can choose from if you simply left-click the Macro box to the left of the "Name" box when writing your macro, if you're on a PS3 I'd imagine you'd have to press some kind of edit key or "X" then arrow Left/Right until you can select the default icon box at the same position. If the icon isn't there at least you can give it a random icon just so that you're not looking at the same gray box with the M on it and as long as you have the (/micon "Physick") command in your macro it will so that icon regardless of what tooltip you have in the Macro list.

Hope that helps.