Frontend is in Java (and Kotlin), indeed, as it's a part of the IntelliJ platform. However, the backend that actually provides IDE features for C# is written in .NET. The backend is actually the same ReSharper logic that runs in Visual Studio but in headless mode.
If you look at the underlying markup, you can see that the web site was designed to be responsive. The sad part however is that it's going to take a bit more time for mobile resolutions to be supported properly.
"Phoning home" is actually not new. We've introduced JetBrains Account as a way of authorizing a product instance (as an alternative to license keys) for a couple of years now.
Current student licenses work exactly the same way, as well as a part of classroom and OS licenses AFAIK. A lot of current personal and some commercial licenses are managed through a JetBrains Account as well.
With the new scheme, JetBrains Account will simply gain more usage than now, hard-coded license keys will eventually go away, but a license server option for environments that have restricted Internet connection will be provided the same as it is now.
Now, there might be certain additional steps we might need to take to ensure license delivery in certain scenarios but we'll be handling this as we receive specific problem reports.
Yes, the change applies to corporate licenses, too. As a bonus for them, there's a transparent model of discounts based on number of licenses and term of payment (https://www.jetbrains.com/toolbox/#commercial)
We're used to helping users of commercial licenses who are faced with delayed payments in their companies, and I'm sure we'll be doing this with the new model as well.
Fortunately, there's a little thing called competition that prevents raising rates at will without facing the consequences, and JetBrains is no exception: we're no monopoly.
I'm sure different product teams here at JetBrains will adapt to the new model in a different way. My hope is that the change will contribute to a focus switch from a race to provide new features to ensuring better stability, performance and UX.
Your understanding of how perpetual licenses with upgrade subscriptions work is correct.
Also, you can still be pretty confident that as a language support by an IDE (PhpStorm in your case) evolves, new versions will be supported by this very IDE, and we don't have any plans to release a separate Php7Storm :)
I was referring to a different kind of change where you might switch from PHP to Ruby, from C# to Java. C# and PHP are naturally not the best combination to support in the same IDE, meaning you might switch your tools as you go from language to language.
On the other hand, as languages and frameworks change, they will not necessarily be supported by your current IDE. In this case, with a perpetual licensing model you're simply left with a license that you don't use anymore, and you're buying a new license to another IDE. With subscriptions, you switch between them as necessary: either by cancelling subscription to one of them and subscribing to another or by maintaining a subscription to all IDEs (which will also be available starting Nov 2.)