[Jules18]

What would the formula be for dihydrogen ammonium phosphate?  I'm just wondering what order it would go in ...

[Tin Man]

I've usually heard to it referred as ammonium dihydrogen phosphate. It makes sense, when you think about it.

You have ammonium ion. Then you have H₂PO₄, which is an anion with a -1 charge.

+1 charge added to a -1 charge...

Make sense now? Just make sure that you're looking at what is actually attached to what. The ammonium is not going to covalently bond with the dihydrogen phosphate, since that would violate nitrogen's octet. So you have ionic left. That's you're clue to look for charged ionic molecules.