The Pinephone sd card is meant for dual booting experimenting new OS’s, and can wipe the internal storage with an image, similar to how you would live boot and install a desktop pc.
I have to say the hardware of Pinephone seemed a bit better than Librem as far as overheating, battery life and being a size closer to every other smartphone that is not a brick of a computer. Purism actually does work on the software that is actually halfway stable (You will want to replace Pinephone’s Qt Manjaro with Phosh/Manjaro). So the benefit of Librem phone is you are paying a developer a paycheck 