In the App Store in the app's Information section, there's a Compatibility drop-down. For Things 3 for iPad, it doesn't show there's a compatible iPhone version, but for Things 3 it shows compatibility with iPhone and iPad. Same with News Explorer: the compatibility list shows iPhone and iPad and other devices.
If you're ever in doubt though, you can also contact the developer by going to the developer website listed in this Information section.
View attachment 967698