It's generally accepted that from a genetic perspective, Paphs and Phrags are too distantly related to be compatible. I wouldn't rule out that perhaps some paphs and phrags might produce viable progeny, but overall, it appears to be very rare.
As already stated, there have been a very limited number of reported successes (defined as crosses that produce viable seedlings, which have then been raised to maturity). And, all of those are debated. The flowers & foliage very strongly resemble the paph parent.
Personally, I'm not convinced, but then I've never seen any of these crosses in person, and I'm obviously not a biologist/botanist who would be able to remark on the results of testing.
I will say that about 10 years ago, I pollinated a maudiae hybrid paph with besseae, and that produced a viable seed pod. However, the flasking company I sent it to said there was no germination.
I think the best reference for these intergeneric hybrids is Phragweb
PhragWeb - Phragmipaphium - Hybrids.