Should I upgrade my phono linestage first or the tonearm for better results?

And on what turntable is this arm mounted? Thanks

Ok so seems you like the Graham line in which case going to the Phantom is probably the way to go. I'd think that $3.5K on the phono side does not get you to the ARC PH8 or Tom Evans Audio Groove + (to quote two great choices on the 'Gon both in the $4.5K range) that would be where I'd like to be -- the choices at $3.5K seems rather "meh" to me and I suspect you'd feel the upgrade bug soon again (of course that's just my opinion, I use the two above as they're both stages I have heard and like, I have not heard all the rest)

In other words I'd optimize from the front end forward, you have the table, you have a pretty nice cartridge now optimize the arm and keep moving forward from that (I've always been a source first guy). I've always believed in pushing as far as you can afford on any one piece and then working on having the rest of the system catch up. It may be that at this point in time upgrading your phono to $3.5K would yield a better improvement than the same on the arm but it could be a dead end whereas the arm upgrade could carry you forward to $10K+ cartridges.

OK. Thanks. My opinion is that you should save your $ and wait until you can commit more money to a substantially major upgrade. The Teres can take whatever arm/cartridge combo you throw at it and $2.5K would not (in my opinion) get you a real upgrade from where you are now (assuming this is $2.5K net of the resale value of whatever you get rid of). If you could go to $4K for example there is a Durand Kairos available at present, in other words I’d be looking at $6-8K arms, and commensurate cartridges and phono stages. Anything short of that you are going sideways, assuming that is you like the kit you have at present.

If you really feed the need to upgrade at present then I’d invest in super setup tools like the SMARTractor, you save the difference and you have something that will serve you going forward
http://www.arche-headshell.de/alignment-tools/smartractor/

Off your main question but if you really have money burning a hole in your pocket you should invest in some proper power cords ( you didn't list any power products)

personally I like Synergistic Research but there are lots of good options out there all easily available used and if you haven't done so you really should invest

Sure there are diminishing returns but in the context of a six figure system and if you can afford a $10K cart then the Phantom could take it! I’m surely not recommending it as a next step and I’d assume you have upgraded the phono stage commensurately before then. 

My own experience was that only once I upgraded my arm (TriPlanar VII replaced by a Kairos) was it that I really found out what my cartridge (AirTight PC1) could do