GrapheneOS support for Fairphone is unlikely to ever happen. Their hardware is too insecure to satisfy GOS's reasonable requirements [1] and have stated that they aren't interested in improving it [2]. Software is also lacking and they've partnered with Murena [3], who has been slinging shit at GOS [4].
On a more positive note, due to the AOSP/Pixel drama there now is a real possibility a different major OEM will be supported: https://grapheneos.social/@GrapheneOS/114711328082841462
[1] https://grapheneos.org/faq#future-devices
[2] https://grapheneos.social/@GrapheneOS/114733211017800480
[4] https://grapheneos.social/@GrapheneOS/114235396540176085