iTunes not showing my iPhone apps

Apple in its infinite wisdom decided to remove app management from iTunes and turn it into the media player/hub that they want it to be. My guess, is that they determined this is where the bigger revenue is for them.

You can read about it here.

Changes in the new iTunes - Apple Support

The good news is that of the app still resides in your iTunes library you can transfer it to your phone via drag and drop. See the section at the end titled Manually add Items from Your Computer.

Manually manage content on your iPhone, iPad, or iPod touch using iTunes - Apple Support

I know exactly what you want to do, and I did provide the link that tells you how to do it. This is a copy and paste from that link. You have to drag the app from the iTunes media folder onto the phone under the devices heading in the side pear of iTunes.

Manually add items from your computer

If you have media on your computer that you can't redownload from the App Store or iTunes Store directly on your iOS device, such as custom ringtones or iOS apps, you can drag and drop the media from your computer to your iOS device using iTunes.

1. Connect your device to your computer.
2. Open iTunes. Make sure that you have the latest version.
3. On your computer, find the item you want to add to your device. If you're looking for Apps, Tones, or Books (for Windows) that previously appeared in your iTunes library, you can find them in your iTunes media folder.
4. Drag the item from your computer to your iOS device in the left sidebar of iTunes.

Should you care to try this, iTunes 12.6.3 can be downloaded and installed over iTunes 12.7. It restores app management functionality.

Read this first. The link to the download is in the article.

http://osxdaily.com/2017/10/09/get-itunes-12-6-3-with-app-store/

If you open a finder window on the Mac and click on your username in the left sidebar go to>Music>iTunes>Media Folder. That folder will show all of the apps that are in your now invisible iTunes library. You have to drag the app from that window onto the phone while iTunes is open. That means that you need to have iTunes running in a window beside the funder window that shows the apps.

Locate and organize your iTunes media files - Apple Support

Maybe this explanation will help. I think that once you locate the media folder, it will be very easy to do.

The New iTunes: How to "Sync" Apps, Books for Windows, and Ringtones