The VNs go like this:

Original Trilogy:

The Fruit of Grisaia -> The Labyrinth of Grisaia -> The Eden of Grisaia

They all got anime adaptations with the same names. I hear they are a fun watch but cut a LOT of content, in particular from the first game (12 episodes for a VN with an an average length of 75h on VNDB).

Phantom Trigger:

Grisaia: Phantom Trigger Vol. 1 -> Vol. 2 -> Vol. 3 -> Vol. 4 -> Vol. 5 -> Vol. 5.5 -> Vol. 6 -> Vol. 7 -> Vol. 8

Takes place in the same universe but it’s an indepentent story, it only contains a few references to the original trilogy.

From the descriptions on Anilist, I believe the first movie adapted the first two volumes of the VN, and the second movie adapted the third volume.