We should push other phone OEM's such as Fairphone and Samsung to work with PostmarketOS, GrapheneOS, and Ubuntu Touch

Talking about Mossad ?

If Google kills AOSP, a lot more than just GrapheneOS will stop being able to exist lest some entity maintains a fork that diverges from Google's path. Vendors that aren't shipping in line with Play Services and the rest of the ecosystem as well as LineageOS and other custom ROM development teams will suffer as well.

This kind of decision would essentially kill adoption of Android in a good number of countries within a few years as well as be the end of Android adoption for anyone that cares about security and/or privacy. Yes, It would either kill or put a large burden upon GrapheneOS as a project, but that is also true for so many other projects in the ecosystem. If the developers shutter their AOSP usage due to upstream abandonment, the users will likely follow in the same pattern.

Governments should require all firmware to be open source. That will do far more to enable linux and other variants than any other game of whackamole. Google will kill Android open-source eventually.

It's weird to group two Linux OSs with an Android OS anyway. One is focused on security, while the others are focused on introducing another type of mobile OS into the market.

I think "push other phone OEM's" here mostly means to encourage these OEMs to make devices that are compatible with these altenative operating systems. In the case of GrapheneOS, that means a device with the necessary security hardware components.