Interestingly, the Librem 5 has two M.2 slots for its wireless comms (one for modem, one for BT/WLAN). This is modular, but at what cost?
In place of an integrated mobile SoC found in most smartphones, the Librem 5 uses six separate chips: i.MX 8M Quad, Silicon Labs RS9116, Broadmobi BM818 / Gemalto PLS8, STMicroelectronics Teseo-LIV3F, Wolfson Microelectronics WM8962, and Texas Instruments bq25895.
The downside to having dedicated chips instead of an integrated system-on-chip is, that it takes more energy to operate separate chips, and the phone’s circuit boards are much larger. On the other hand, using separate components means longer support from the manufacturers than with mobile SoCs, which have short support timelines. According to Purism, the Librem 5 is designed to avoid planned obsolescence, and will receive lifetime software updates.
I haven’t been able to find NXP i.MX 8 on Geekbench. The quickest I could find is i.MX 8 QuadMax. It has 4x Cortex A53 1.2 GHz and 2x Cortex A72 1.6 GHz. 64 bit ARMv8, the A72 is 16 nm (compare with SD 750G 8 nm), while big.LITTLE it is only 6 cores. FP3 with SD632 has 8 cores, 4x A73, 4x A53, with higher GHz and 14 nm. A Librem 5 only has 4 cores of the A53 series at 1.5 GHz.
Performance-wise, if we look purely at CPU power, a Librem 5 is a downgrade compared to a FP3 (from 2019 with SoC from 2018). And the successor in the i.MX series isn’t much better. Depressing…
(I did check other features like WLAN and GPU but don’t have time now.)
Pinephone has an Allwinner. The successor Pinephone Pro (with one month warranty its meant for developers) sports the following (taken from website): The PinePhone Pro is the end result of this journey. It is powered by a Rockchip hexa-core SoC operating at 1.5GHz, and ships paired with 4GB of dual-channel LPDDR4 RAM as well as 128GB of internal eMMC flash storage.
IIRC it has a rk3399, RK3399 - Rockchip Wiki which has 2x A72 and 4x A53 at 28 nm (less performance than FP3). Another source: Rockchip RK3399 (OP1) | Processor Specs | PhoneDB
Of note, Pinephone Pro has near mainline Linux support.
I didn’t check MTK… Their track record is worse than QC, but I don’t want to dismiss them (they are #2 in this space and deliver serious horsepower)
Regarding FP2, Leo is making a USB-C replacement bottom module for it. But you can’t order it anymore.