When should you watch Fairy Tail the Movie Phoenix Priestess?

The movie "Fairy Tail the Movie: Phoenix Priestess" is set after the events of the Tenrou Island arc and before the Grand Magic Games arc in the Fairy Tail anime and manga series. In the English manga release, it would be equivalent to right before Volume 32. For the anime, it would be episodes 175 and 176, which are included in Season 6.

So, to watch the movie in chronological order, you should watch it after completing the Tenrou Island arc and before starting the Grand Magic Games arc in the anime or manga series.