This is a perenial phlox so it is unlikely to flower in the first year. it might even be the second or third year before you get a flower.

Sorry Mr B, I disagree slightly. Even a small weedy plant of P. paniculata will usually produce a couple of flowers at the tip of a stem. If it is a young plant, you should get flowers the following year if none this.

Agree with Fractal, all the ones we have ever planted have flowered their first year, even when they were poor specimens.