This is surely the closest to a solution we have, IMO. An alternative to the Android-iOS duopoly that involves futzing with cables and command lines is never going to go mainstream. By contrast, a vertically integrated FOSS(ish) hardware-software stack might eventually get to 5% market share, like desktop Linux. At which point companies and governments will be forced to take software freedom slightly more seriously. That's my optimistic take.
https://proxysto.re/en/ sells GrapheneOS phones, with worldwide shipping I believe. They do donate a portion of every sale to GrapheneOS. However, you're recommended to install GrapheneOS yourself and not buy it from someone else, so that you know it hasn't been tampered with.
You can verify it was installed correctly using boot hash+attestation+factory reset. Much easier to just install yourself though. They have instructions for verifying.
Many services sell phones with GrapheneOS preloaded. Can be easily verified but no benefit for most people so it probably doesn't glow.
Proxysto.re seems to list good services as well and minimizes data. Accepting Monero is positive for their trust as well.
You are asking if a partnership with Fairphone would bring in revenue for GrapheneOS.
Fairphone would need to design a new phone with hardware that meets the security requirements of GrapheneOS, which is what Motorola is doing in the announced partnership. There is the development cost, and then the new phone hardware would be more expensive than the Fairphone 6. For Fairphone, there is the question of whether the cost of developing this new phone will be recovered in sales of this more expensive phone.
Would Fairphone give GrapheneOS a big enough share of the profits to fund the port of GrapheneOS to this new hardware and pay for the share of the costs of the monthly software updates? Otherwise it wouldn't reduce GrapheneOS's need to fundraise via donations, which is the subject of this thread.
I don't know if Motorola is offering any cash to GrapheneOS, but they are a famous enough manufacturer that the partnership will raise the profile of GrapheneOS and help them be more successful. By contrast, I'm not sure how many people have heard of Fairphone but have not heard of GrapheneOS. The only reason I've heard of either project is through tech social media. Retail outlets in my area don't sell Fairphone and local mobile operators don't offer Fairphone hardware. But these guys do offer Motorola.
In summary, I'm not sure a Fairphone GrapheneOS partnership makes financial sense for either project, even if it sounds great from a tech nerd perspective.
Fairphones have very poor security at a hardware, firmware and software level. They've shown complete disinterest in making devices meeting our requirements.
Fairphone is closely partnered with /e/ and Murena which have repeatedly claimed GrapheneOS mainly benefits criminals and pedophiles. They've also said that about hardened devices in general on several occasions. They've falsely claimed GrapheneOS is mainly used by GrapheneOS. That's part of years of misleading people about what GrapheneOS provides to promote their products. Fairphone stood by them on this.
It's very relevant the context leading someone to post this thread. /e/ and Murena directly got involved in attacking us during the attacks on GrapheneOS with misinformation in France by a national law enforcement agency. Many of the claims made to attack it closely resemble years of past attacks by /e/ and Murena falsely framing it as being for criminals and not suited for regular people.