I think this episode mostly just develops on a lot of the things that we all already discussed in the episode 2 thread. Many of the themes of Phos wanting to be reborn are repeated, issues with Cinnabar, issues with Dia and others. A continuation of character development while also providing ample action.

Notably the episode continues with its trend of doing amazing things with its 3d usage that are just completely and totally impossible in traditional art, some examples:

This reformation scene. A good example of how the show uses thing that don't actually happen to illustrate that the depictions are emotions. Phos is reforming as a liquid here but we know that the gems actually piece her back together in chunks. This is about the mental state of Phos. I think it also has some magical transformation influence? It might indicate that this is also a moment in time something within her biology (gemology?) is changed from the process of being eaten and reconstituted by the snail, this might be known to manga readers, I've avoided reading it until we know a new season isn't coming so I don't know.

This forest running scene. Nothing fancy to analyse about it, it's just gorgeous and you can't expect to replicate it within a hand-drawn medium. The cinematography is fantastic.

I would link the battle scene too but I can't find a source for it unfortunately.

There was a really nice scene right before they pull the snail up where we get a glimpse into Bort's secretly underlying deep care for the other gems (especially whatever pleases Dia except putting herself in danger) when Dia tells her, in the middle of the night, that she knows how to save Phos. Even though everyone seemingly dislikes Phos' attitude, behaviour or lack of contribution to this society they still all protect and care for her.

As for Phos being able to talk to the snail. Quite possibly the most useless thing to gain from the situation I can think of.