I found limited success or usefulness for whirlwind on mandi. Until Mandi gains access to foul play, it's best set is probably closer to
Knock off/roost/defog/taunt
In OUPokebank, Mandi is deadly simply by foul play. It doesn't NEED to phaze for the majority of the time because it can cripple physical set up sweepers and hurt special pokes a bit with knock off. So that is something to look forward to.
Mandi should be looked to as a phazer in only few situations, in teams where another devoted phazer does not exist and a phazer is needed. The weaknesses to ice, electric, as well fighting and bug on roost turns, make it rather prone to getting the bad end of a phaze in. Also remember that the primary purpose of mandi is to remove hazards. If the hazards are gone, using mandi as a stall poke doesn't work well. Personally, if you want a phazing defog user, you'd be better off with skarm. Mandi fills in more geared towards removing items and more speedily taunting walls.