For comparison Bunnie's Precursor [i] (FPGA RISC-V mobile) is slated for ~2yrs of development, and he's someone who has the connections and know-how to trim the delivery schedule as much as possible.
It's not - it's pretty much a regular unlocked Android phone in this regard, which is why it was stuck on old Android version for a while. Other OSes work there by using Android compatibility layers. It is a very interesting and noteworthy project because of other reasons that you already mentioned, but FLOSS-friendliness of its components isn't one of them (which isn't surprising, as this requirement limits your available choices quite a lot; and so do the Fairphone's other requirements already).