Plane Cards are for a specific type of magic game called planechase. this should explain it: http://wiki.mtgsalvation.com/article/Planechase

You basicly play a regular game with a regular deck and next to it you have a deck of 10 plane cards. at the beggining of the game you open one and from now on it is active until it is replaced. In order to replace it you must through a 6 sided die and get a planeswalking symbol, then the plabe is switched. If you get the chaos symbol it's effect on the plane accures. in order to throuw this die you must pay 0 mana, and it costs one more for every time you want to use it this turn.

BTW I have not seen a Phrixia plane card. I have heard of an upcoming new phryxia plane card upcoming. Anyway I would like some proof of this card or I'll just have to assume your making this up :)

edit: oh! you meant the forth sphere! (blushes...)

4th sphere works best with a monoblack deck or the zombie deck that the plane card came with. Planescape is a pretty fun element added on with your regular games, ust hope you use the right planes.