I just don't see this happening with Phoenicia. For one, although the civs in GS are gimmicky, they all adhere roughly to a consistent gimmick pattern. Terrain bonus. One or two additional unique units/buildings. And usually a downside. A city state civ would break from the consistency. And the idea is of a substantially higher complexity level that I think they would save it for expack 3.
Yes and no. While there has been a Pattern for all the Civs in Civ VI, GS breaks this pattern completely with the Maori, by giving them a Mobile Sea start: a very different mechanism from any Civ in any Civ game that I know of. Now, this may be a 'one off' experiment, but I doubt it, and I think it indicates that the Pattern is apt to be broken or bent by future Civ inclusions in the game.
For two, a city state civ within VI would emphasize the individual specialties of each city state, given the way districts complement CS types. And although Phoenicia had religion, and a military, and science, it wasn't very cleanly divided into specialty superpowers and was indisputably a trade civ first and foremost. It could receive unique luxuries as proposed earlier, but on face value that would be underutilizing the idea of a city state civ.
There have been several attempts in Civ V and Civ VI by Dodders to implement a variable City specialization or 'City State' Civ. In Civ V there was an Olmec civ that was pretty much as I described, each city other than the original capital built its own units and went its own way, but didn't coast any maintenance for anything to the iv, until you decided to 'incorporate' them, at which point they became 'regular' cities. Not completely adaptable to Civ VI as is. Another attempt was a Tribal Civ: the Civ VI version of the Iroquois in which as each city (including the capital) is settled, you pick a Specialization for it: military, cultural, trade, religion, etc. This is another step in the right direction, but doesn't really represent the independent streak inherent in any Civ composed of autonomous cities/city states.
The point is, there are attempts and models that can be used, and of course a current City State model in Civ VI that can be modified to represent a Civ.
And I don't think the city state idea fits Phoenicia, at least when you step back from the idea and look at how Italy is begging to take that role. While you could stretch Phoenicia to fit the idea and people can squint and accept it, it isn't as resonant as Italy with a scientific Bologna, cultural Florence, commercial Venice, industrial Genoa/Milan, religious Rome, and militaristic Naples. Perhaps multiple cities of each kind to fill out a city list.
While the Italian Renaissance City States may be better known to the Eurocentric Western histories and historians, it merely points out the similarities between what I consider the three great 'City State' Civs: Italy, Greece and Phoenicia. All three were cultural entities: language, religion, culture, were similar enough that the individuals in all their cities and polities thought of themselves as Italian, Greek, and Phoenician on some level, even if on a practical level day-to-day they were Venetians, Athenians, Sidonians (Sidonites?)., etc. On the other hand, despite cultural identity, none of them had any political unity until they were conquered by Someone Else: in the case of Italy, mostly Austria/HRE, Greece by Macedonia and later Rome, Phoenicia by Persia and then the Diadochii.
Which points out the problem with a 'City State Civ'. Unless the design provides a rather unhistorical military unity among the various cities comprising it, the Civ will be snapped up by the first Unified Civ that comes along. On the other hand, looking at the tremendous commercial, scientific and cultural diversity and influence all three of the City State Civs had, I think a case can be made for some kind of Built In Bonus to a city state Civ in those areas. They may have a great deal of trouble being a military aggressor, because no one City has the power base for it, but they should be able to defend themselves ferociously (see Alexander's Siege of Tyre, one of the great Epics of Siege Warfare) and should have enormous influence culturally and scientifically.
I might argue that it's even more appropriate for Tyre, which did a lot more colonizing than Byblos did, though I can see where you're coming from with Byblos and the diplomatic angle.
I know, everyone else in the region is -ite except the Phoenicians and their constituent Sidonian, Tyrian, and Byblian peoples. 
