Having dealt with this personally, I can guarantee that CAF/RDOF require phone service to be provided as an option (and no, pointing a customer toward a third-party voip service doesn't count) to both have an area counted as "served" (so that you're not overbuilt) and providing phone service is a condition of these programs.
At this point I'll point out the ridiculousness of the FCC pushing network neutrality at the exact same time as forcing companies who take these grants to compete potentially unfairly with internet-based voip providers.
My understanding of the reason is that CAF/RDOF are actually *telephone* programs which have been extended to do internet. It's more telephone w/internet added on than internet w/telephone added on from a policy standpoint.