To continue with the story, head over to Astral City. You have to make your way back to Eckdart then sail to Tropp. From Tropp, walk all the way back to Tatroi. Once you’ve reached Tatroi, you can take a ship to Astral City.
Once there, approach the castle. If you haven’t recruited Phia earlier, she’ll welcome your party by the castle doors. At this point, if you have six characters or less in your party, you’ll have the option to recruit her. This is going to be your last chance of recruiting her.
Whether you recruit her or not, you’ll get an audience with the King of Astral. During this meeting, you’ll receive the Astral Emblem. You have to return to Tatroi next.