I dropped my i phone in the pool

Did you power the iPhone off immediately and leave it off for at least several days or placed the iPhone in a bag of uncooked rice for several days at least?

If not, it is a matter of time before worse will happen. That message indicates moisture damage to the lightning connector port.

The store won't fix it. The interior of the iPhone got wet and electronics and a little water or moisture don't mix much less being completely submerged in water. Drying the outside alone and leaving the iPhone powered off was not near enough for any chance at salvaging it. It may work for a while but only a matter of time.

Apple offers and out of warranty or not covered under the warranty repair price, which pays for exchange at a significantly reduced price off the full retail sales price.