Have you seen this thread?
Up to now, there is no sailfish. But you can get the FP3 with /e/ preinstalled.
Sailfish will depend on community-efforts and from what I found on the sailfish homepage, there is nothing underway so far.
It was already requested but did not make it to the list of nominated target devices
And it is - of course - not on the list of adaptions:
Edit: Update [2021-01-27]:
No new developments to be found. This posting on the new sailfish forum even makes it look less likely, that official Sailfish OS will come to the Fairphone 3. (Though I have no idea regarding the credibility of that user; sine I am not active on that forum.)