took a sample to a pool store . . .
Bad idea. You'll soon trust your own testing more than a pool store, and you'll be 100% justified in doing so.
and the phosphates reading was 1810.
A touch high, if true, but their testing is not even remotely reliable. Remember, also, that phosphates are measured in parts per billion, not parts per million. If you're really concerned about it, you can get a Taylor K-1106 kit. It won't pretend to have the kind of granularity the pool store test pretends to have, but it will be reliable. This
wiki entry is informative and reliable.
( The pool store said that if we lowered them the FC would come up)
FC comes up by adding chlorine. I'm not aware of any mechanism by which lowering phosphates would increase FC, but I'd be willing to defer to more knowledgeable members on that topic. I'd actually appreciate being educated on such a thing, if it exists.
I read on TFP that phosphate doesn't matter as long as I get my FC in range.
Treating high phosphates is 100% optional. I like
@bobloblaw42's analogy
above (and username). I might go even stronger than "bouncer", though, and say "assassin".
Except for rare and unusual situations. What would a rare or unusual situation be?
If you had a difficult time maintaining a good FC to CYA ratio. But that would be rare and unusual. If you don't have to be away from your pool much, and you stick to liquid chlorine (dichlor or trichlor tablets only when you're going out of town and only when your water has room for the CYA), you're not going to have any problems with a good FC to CYA ratio.