I have both. Shroom is more of a tan shimmer that looks more natural (as if the light hits the exact spot where you put it but doesn't change the colour of your skin, just makes it glowy), whereas I think Phloof is basically a shimmery [almost] white. I like to use Shroom as a brow highlighter or even an all over colour sometimes. Sometimes I also use it on my cheekbones as a highlight. I like to use Phloof on my inner corners mostly. I also use it as a brow highlight for more dramatic looks because it's a lot lighter in colour than Shroom.
Hope that helps =)
*Edit
Oh, originally I went to the store to buy just one because I needed a shimmery brow highlight. I thought the two looked really different on the skin (they look the same in the pan) which is why I bought both. Shroom could be used as an all over colour for a shimmery neutral eye (like with Satin Taupe and Mulch, which I did the other day). Phloof could be used if you were looking for a shimmery whitish colour. Once I used it all over my lid with Creme de Violet and Sketch and it looked like a white lid with purple smokeyness
*Edit again!
Sorry! Forgot to add... For reference I'm NW30