The pinephone like the librem5 has hardware kill switches so you can operate with the baseband off whenever you don't need the cellular network enough to justify the risks.
I don't know if the Librem5 goes beyond what the PinePhone is purported to do here:
"The LTE modem on the PinePhone is a ‘black box’, and runs its own Linux system internally. This includes all the proprietary modules (blobs) needed to run the actual cellular radios. However, this system is almost entirely isolated from the main system running on the A64 SoC. The only data contacts between A64 and modem are USB connection for data and I2S connection for audio. All data going in or out of the modem must go over these connections.
There is no RAM or flash storage shared between the systems. In short, unless you explicitly send data to the modem, it is never in contact with the blobs running inside it. The modem cannot send any data to the phone unless phone is willing to receive it (that’s the basics of USB)." [0]
That's in addition to the kill switches.
There might be other blobby aspects of the SoC/peripheral support story that the Librem5 gets better than the PinePhone, I haven't dug deep there.
Both Pinephone and Librem 5 have open GPU drivers and boot firmware. However they have proprietary WiFI/Bluetooth drivers. For the latter, Pinephone is using blobs in Linux, while Librem 5 made the firmware part of hardware (non-updatable), trying to get Respects Your Freedom certification from FSF.