Can the Photon Barrier Block Ultimates?

It has the exact same behavior as Reinhardt's shield and Winston's bubble shield (and any other energy powered shield for that matter) so yes it should block both of those ults, although Earthshatter could go through the shield if it's not touching the ground (same as if Reinhardt is looking up).

Yes, Symmetra's Photon Barrier acts like Reinhardt's and Winston's barriers, and will block anything those two barriers block. Specifically, it will block Earthshatter if it's touching the ground, and will block Self-destruct if you're fully covered by it.