Tallen, I know at least Phlox drummondii are annuals.

Here are some annual phlox that I started from seeds this year. They are from a packet called "Star Mix."

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If it's Walmart, I'd wager it's the perennial Phlox Subulata - espcially if the foliage is low and mat forming. Depending on the conditions the supplier grew them under, they could be brought into bloom at times other than spring. Mine bloom heavily in the spring and start up again with a less heavy flush in the fall.