Specifically the Phoenix as seen in "Star Trek: First Contact". What would Zefram Cochrane's Phoenix look like in the TOS style
I, personally, have very little trouble accepting First Contact's Phoenix as part of the visual/aesthetic continuity of TOS. The smooth hull appearance of TOS is a more advanced appearance borne of the function of making everything accessible from the ship's interior rather than require extra-vehicular activities. The Phoenix, on the other hand, was designed as a thrown-together prototype designed to "just get it to work". Form should follow function, and it's logical that a small ship designed and built on the ground should have lots more exposed conduits and "greebles" than a full-sized starship like the Enterprise. It's the Apollo moon lander of its day compared to the Space Shuttle! Having said that, it might be fun to think about how Matt Jeffries would have approached the Phoenix's design. I'm reasonably sure he'd keep the bell nozzle at the end of the ship. He might keep the stage separation after launch, since that was a common feature of Apollo-era designs, but he was also of a time when science-fiction typically imagined space vehicles with single-stage-to-orbit capabilities. So I'd argue he'd go for a more streamlined rocket with a smooth capsule, possibly with two fixed-fins starting halfway down serving as struts for the warp engines. A third fixed-fin would balance out the symmetry and support a domed radar dish. If Roddenberry told him it looked too much like something Chelsey Bonestell would do, he might adopt the idea of extendable drive units that stretch out like they do on the First Contact version, but there'd be no fairing separation to reveal the engines -- at launch, they'd be housed in exposed recesses on either side of the fuselage and extend in orbit. A radar dish would pop up after being folded back against the fuselage.
Are we all just talking (thinking?) past the initial question? I took it to mean "what would the combination of shapes that makes up the Pheonix look like with a smooth TOS style exterior and maybe some other Jefferies style modifications?" as opposed to what it would look like if Jefferies had designed it or how it fits into Trek chronology, etc.