Yep, that's a D&A T-600. Basically it was one of the final versions of the Phantom. As D&A amps go they are somewhat of a rarity but as to what it's worth - well, something is worth what another person will pay for it.
It looks to be in good physical condition so that's a plus but the question is how well does it work? What's the tube complement? Probably has 10 6LQ6s in it and it may or may not have a keying tube.
D&A were well known for building amps with whatever parts they could get a lot of on any given day. It's why you never see an official schematic or service manual for them.
If the thing works well, hasn't been golden screwdrivered to death and is as clean inside as out, I'd say to the right person it should bring somewhere between $350-$475 depending on how strong the tubes are and how much the buyer wants it.
Maybe you will get lucky and find a hardcore D&A collector who needs this model to complete a collection!