Why did Apple skip the iPhone 9?

Every answer here praising Apple like they’re some kind of marketing genius or something. No, the truth is that Apple isn’t very consistent with their naming. Period.

Let’s take a look at all the iPhones and see the reasoning behind those names

iPhone – this is the first iPhone and as such, this naming is totally appropriate. Otherwise known as the first iPhone or iPhone 1.

iPhone 3G – this is the second iPhone. there was no iPhone 2 because the biggest feature of the second iPhone was 3G connectivity therefore it was called the iPhone 3G. This is the only time the iPhone was named after one of its technology features – and set the naming scheme for the next decade.

iPhone 3GS – this is the first time the ‘S’ was added denoting ‘speed’. In the future, iPhone models with the ‘S’ appended are usually incremental upgrades, with the S standing for the signature incremental improvement which is usually the processor/ram i.e Speed.

iPhone 4 – Because the second iphone was named the 3G, the next iPhones all follow in numerical order. Not only that but this really was the 4th generation iPhone, so the naming here makes sense. The form factor was also changed here, from curved sides to rectangular sides (IMO my favorite design). Design changes are usually denoted with (but now always) new iPhone (non S) numbers.

iPhone 4S – a speed and camera upgrade, and also adding Siri support, it makes sense for this model to be denoted with the ‘S’ added to it.

iPhone 5 – A display change from 3.5″ to 4″ along with the change to a lightning connector, as well as the first to support LTE, is the major differentiating factor here, warranting a new iPhone number.

iPhone 5C – this is the only time the iPhone has used a ‘C’ appended to it – this was meant to be the ‘cheaper’ version of the iPhone 5S – but the ‘C’ was never used for their ‘cheaper’ models ever again..
Edit
: I’ve been told that the C stands for “colors” not “cheap”. It still doesn’t make sense. Other iPhones have colors too. They never used C again.
Edit 2:
Ok I’ve been corrected again apparently it stands for ‘vibrant, bright colors’. Allow me to roll my eyes. In any case, it’s no less inconsistent and thus my point still stands.

iPhone 5S – a speed and camera upgrade, as well as introducing TouchID. No changes in design. These are noticeable incremental upgrades, so it makes sense for this model to be denoted with the ‘S’ added to it.

iPhone 6 – A display change from 4″ to 4.7″ is a design change, therefore warranting a new iPhone number.

iPhone 6 Plus – This was the first time the iPhone was offered in two different sizes at once. The ‘Plus’ model uses a 5.5″ screen but in every other respect was the same internally. Future ‘Plus’ models usually had a better camera upgrade.

iPhone 6S / 6S Plus – These were significant processor/camera upgrades that kept the iPhone 6 design, so it made sense for these models to be denoted with the ‘S’ added to it.

iPhone SE – I’ll cut Apple some slack here. Whether the SE stands for ‘Special Edition’ or ‘Small Edition’ this was meant to be a different line of phones. Although I think iPhone 6S Mini Would have been a better name and aligned with their iPad products more, as well as denoting the generation it was from.

iPhone 7 / 7 PlusThis is where Apple starts to become more inconsistent. There are design changes but they are not substantially different from the iPhone 6 design. The biggest difference externally is the removal of the headphone jack. Does that warrant a new number upgrade? Not sure. IP67 resistance is finally added. The Plus model (deviating from previous Plus models) has an extra telephoto lens. These are all internal upgrades – meaning the iPhone 7 / 7 Plus should not be a new version number, it should be another ‘S’ model, but since Apple obviously doesn’t want to name their next device ‘iPhone 6SS’ that’s why they bumped it up a number despite no design change.

iPhone 8 / 8 Plus – Why did this need to be a version number change? There is no design change at all, it looks identical to the iPhone 6/6S/7 and should really be called the iPhone 7S but I suppose the reason why Apple bumped this version is up, is because the iPhone X was released at the same time, and 7S and X seem to be too big of a gap (although they are skipping 9 anyways). So yeah.. this is a bit weird. It’s a purely hardware upgrade.

iPhone X – they released this at the same time as the iPhone 8. Granted, it’s a redesign – the screen is now a 5.8″ bezel-less albeit with a notch, and removes the home button in favor of FaceID, so it warrants a version bump. However, this is technically the first redesign of the iPhone since the iPhone 6. This should really be called the iPhone 7, not the X as the previous phones were all ‘S’ upgrades. But they went with 7, then 8, and then skipped 9, probably for the same reasons why Microsoft skipped Windows 9 (it sounds bad compared to 10 I guess as 10 conveys a much heavier upgrade, 9 just screams ‘almost there’), and they went straight to X, using a Roman numeral instead of an Arabic one no less.
Some dude answered below with ‘oh Apple changed their entire naming scheme and they are simplifying and unifying their naming with their computers now! no more S/Plus models!’ How wrong you were.

iPhone XS / XS Max – Oh boy. Back to the ‘S’ naming again. It makes sense this time because XS is an incremental upgrade – but why the XS Max instead of XS Plus?? In the future Apple has now changed their ‘Plus’ naming for their bigger models to ‘Max’ now. Ok… so XS Plus doesn’t roll off the tongue as well? I don’t think its a big difference.

iPhone XR – This is just weird. If this is supposed to be the cheaper model.. why not use the ‘C’ naming from the 5C? the XC doesn’t sound that bad. Instead it’s ‘R’ for some reason. I have no idea what the R might stand for. It has this ‘liquid retina’ display but that’s just marketing talk for Apple’s standard IPS display.
Edit: Someone told me it’s because the ‘R’ comes before ‘S’ in the alphabet and this is the cheaper model thus it’s the R. Wow. They did not use this naming for the iPhone 5C (cheaper than than the 5S) or the iPhone SE (cheaper than the 6S), and somehow I’m willing to bet Apple will not name the next cheaper model the 11R. It just sounds so weird. Sounds to me that like the 5C, this is a ‘one off’ naming.

iPhone 11 Pro / Pro Max – Back to Arabic numerals again. Ok.. and just to be clear, the new flagship model has the ‘Pro’ appended to it. What’s ‘Pro’ about it? An upgraded camera with a new lens. Ok… first of all why does that make it more ‘Pro’ than previous iPhones, and why does it warrant a version number upgrade? The design is unchanged from the iPhone XS. And now you have ‘Pro Max’ as well… this naming is really getting out of hand.

iPhone 11 – yes this is the successor to the iPhone XR as the cheaper model (the Pro model is the flagship). And no, I have no idea why it’s the 11, should be the iPhone XRS right? incremental upgrade, no design change.

So there you have it, Apple is inconsistent with its naming.

In particular I take issue with:

iPhone 3G – named after a technology in the phone, this was never done again

iPhone 5C – the only time they use the ‘C’, they don’t use it ever again for their ‘cheaper’ models or other colored models..

iPhone 7 – not a redesign, but gets a version bump

iPhone 8 – not a redesign, but gets a version bump

iPhone X – uses roman numerals, skips 9

iPhone XS Max – Uses Max instead of Plus for some reason

iPhone XR – why the R?? that’s just random.

iPhone 11 Pro – Where did the ‘Pro’ come from? It’s not more ‘Pro’ than previous upgrades were. And also not a redesign, but gets a version bump.

What’s their next phone? iPhone 12S Air Max?