Yeah... but why? What attribute do you think is unique to people with PhDs?
Regarding projects which receive a grant, holding a PhD does not matter.
What a Phd recognizes, and is relevant to the project at hand, is the ability "to produce original research that expands the boundaries of knowledge".
(Per Wikipedia: "Because it is an earned research degree, those studying for a PhD are required to produce original research that expands the boundaries of knowledge, normally in the form of a thesis or dissertation, and defend their work against experts in the field. The completion of a PhD is often a requirement for employment as [...] a scientist in many fields.")
If you know this, and know that people without one can still produce original research that expands the boundaries of knowledge (even giving your own examples) then why do you require one?
Moreover, as it is a voluntary function, no one is harmed financially by this constraint.
If this foundation does not have such an overhead and will never create cozy director posts, cozy diversity officer posts etc., then this is a huge credibility boost and I'd mention it on the website (with the explicit promise!).
But then the foundation has to stick with it and not stealthily sneak in CoCs and people after a while.