Hi Joe and welcome to the forum. There are other topics on this so this may get moved to one of those.
Faiphone do not have resellers outside the EU/Uk etc but there are resekkers in the UK, for example that will post to the USA and cover the warranty.
See the following for those that sell internationally, noted by the
Clove may be a good place to start.
Other topics to read
https://forum.fairphone.com/search?q=networks%20usa