As you know, iTunes 12.7 gave up support for managing Apps (Changes in the new iTunes - Apple Support). You have two options.
1. Download your previous purchases directly to you iPhone - see the "On an iPhone, iPad, or iPod touch" subsection(s) in:
2. Uninstall iTunes 12.7 and install iTunes 12.6.3. See the "iTunes 12.7" section in: