Where's the iTunes app section for my iPhone?

You can find a overview/summary of iTunes 12.7 changes on this Apple support page.

Changes include:

• Apps: Looking for your past iOS app downloads? Learn how to redownload apps on your iOS device.
• iTunes U: Collections of iTunes U content appear in the Podcasts section of iTunes.
• Internet Radio: Your Internet Radio stations appear in your music library's sidebar. Click Edit in the sidebar to show or hide Internet Radio.
• Ringtones: iOS 11 supports redownloading ringtones directly to your iOS device, without the need to use iTunes on your Mac or PC.
• Books on Windows: Books on iTunes for Windows are managed in iBooks for iOS. Learn how to redownload books on an iOS device.

If you have an iOS app, ringtone, or book that's no longer available for redownload, you can move that content to your iOS device while plugged in to a computer with a USB cable.

According to MacWorld:

Where it will really hurt is if and when you need to restore an iPhone or iPad. You can still perform iTunes backups, but the restore won’t transfer apps from your Mac, but instead re-download them over the Internet from Apple. That can easily consume gigabytes of bandwidth, depending on your app choices. Many users download few apps, or those apps that are relatively modest, and this won’t be as big a hit.

There’s no way to bypass or minimize this problem. If you have any kinds of restrictions on your internet service—whether in performance or limits—you should consider using a public Wi-Fi hotspot or the Wi-Fi of a friend without those limits. You’ll need to plan ahead when you wipe and want to restore an iOS device.

So to answer your question, that section (apps) has been removed from iTunes, and restoring apps will require redownloading via the AppStore in iOS. Plan on using Wi-Fi or a hotspot to prevent large data usage when redownloading apps.