Upon arriving at the moon, Phos somehow thinks that by telling the gems that there's a way to bring the gems back, that they'll actually understand. Phos is at the moment seeing the bigger picture, and his plans are all fuelled by desperation. The other gems, save for Pad, don't see the bigger picture. They aren't thinking long term.
Phos wants to bring the dead gems back as much as they do, but he's aware that he needs to negotiate strategically with Aechmea, because he literally has no power over him, as far as he himself knows.Aechmea of course is doing the long con with the eye, but Phos doesn't know this.
When the other gems find out that Phos hasn't already asked for the dead gems to be returned, they're shocked, and Phos, being put on the spot has to play all his cards immediately.
This is another example of Phos not being able to put himself in other people's shoes.
Later, he doesn't listen to Yellow when Yellow repeatedly says that he doesn't want to go to earth to fight. This is played comedically, but it does show that Phos doesn't really get that no means no, unless it's told to him upfront, same thing with Craig.
Pad helps convince Yellow to go anyway, but it backfires when Yellow can't handle the situation and ends up just freezing up, which might very well have fucked the entire raid.
Phos has never had any self value, even before the Winter arc, which is made clear by how he says to Ventricosus that he's useless, so it doesn't matter if his body ends up being destroyed in the ocean or not. Phos believed that he was useless before, (most likely due to the way he was being treated by everyone else), and saw himself as worthless, so it didn't matter what stunts he pulled, because to him, no matter the end result, it would always be "and nothing of value has been lost haha xd".