I swear, the FSF has no concept of onramps, incremental victories, or provisional compromises.
Graphene, iode, and /e/OS exist, in addition to LineageOS. Are they "free enough" for the FSF? No, but to argue that the reason these things don't have mass acceptance is because users can't modify their modem firmware is patently absurd. I can appreciate the desire for purity, and a truly Free/Libre software stack from the low-level firmware to the apps, but this is absolutely the wrong starting point.
For starters, they could throw some funding toward F-Droid. Fund app development contests to improve availabilty of FOSS/FLOSS mobile apps. Users won't move off a proprietary OS if they *also* have to say goodbye to their massive app stack. If apps are available that will allow users to migrate their data to FOSS alternatives that are *also* available on a FOSS/FLOSS mobile OS, the migration path off Google Android becomes much easier to walk.
To double-down on this, the FSF could fund Creative Commons alternatives to Spotify and Netflix and maybe Tiktok or Instagram, and provide music and video streaming platforms for artists to post their music and movies (maybe with a self-hosted/federation option). Sure, it'll be a bit amateur at the beginning, but so was Youtube, and now entire careers exist because of it. If the FSF got behind these kinds of platforms, to the point of releasing iterations of streaming clients in the Google Play and Apple App Stores, it would chip away at the reasons *why* a FOSS/FLOSS operating system has such an uphill climb. Imperfectly, sure...but my wager is that more users would be willing to abandon iOS and Android if they already move over to independent streaming apps, than if the FSF's sales pitch is "you can modify your own firmware".
From there, again, onramps. Make a list of phones that pass certain criteria of freedom - 'copper' for phones with user-unlockable bootloaders and a commitment to release device trees within the first year, 'bronze' for phones that ship with unlockable bootloaders and release device trees on day-one for Lineage-and-friends to modify, 'silver' for phones that ship with unlocked bootloaders and officially supported mostly-Free Android builds with user instructions to load it, 'gold' for phones that ship with a mostly-free Android build out of the box, 'platinum' for phones that are FOSS everywhere except the modem (which has a documented API), and 'diamond' for 'no proprietary code anywhere, at all'. Hell, the FSF could probably make a few extra bucks reselling such phones at all the different levels, and let users decide the level of freedom they're looking for.
Ultimately, starting at the lowest level of the hardware stack might have its place, but it is of no virtue if the LibrePhone has no users (or worse, whose primary users are troublemakers who get IMEI runs blocklisted). Firmware is the least of the problems the FSF is facing, and while a staunch adherence to principles is laudable, it is of no virtue to have an OSS cellular modem that can't make phone calls or text messages because no telco will allow it. It is of no virtue to have a FLOSS laptop who spends its day storing data in Google Drive, acquired from Salesforce, and copied into Quickbooks Online, then going home and listening to Spotify and watching Disney+...and the phone landscape is exactly the same. Without a counterbalance of enabling users to meaningfully interact with their data without being beholden to proprietary systems, the FSF will be the poster child for winning the battle and losing the war.