I just cannot see even a prime Flex beat Phil. Heath's BDB is above Flex's, way more complete, same with the FDB. Flex's MM crab exposes the same weakness: narrow clavicles and Phil has the conditioning advantage. Shawn is not close on anything.
Both Phil and Flex are narrow thru the clavicles. It was Flex's round muscle bellies that take it. Plus, if you ever have seen Flex hit a FDB, he does it in a way that adds drama to the pose, accentuating his smaller waist. Phil has large obliques, which take away from his taper. Also, Flex smiles, Phil makes weird faces, all these things add up.
Don't get me wrong, I am a Phil Heath fan, and if Flex and Phil were competing today---using Flex as yesterday and his mentality, Phil would probably beat him, due to Phil being more consistent wig his conditioning.
But Flex of 92,93, 97, 98 would be very hard to beat by Phil of today.