This feature, introduced in iOS 11, has been moved, in a very Windows-esque fashion, from Settings->General->iPhone Storage to Settings->Apple ID, iCloud, iTunes & App Store->iTunes & App Store.
I call this move Windows-esque because it seems the biggest change between versions of Windows is they scatter all of the settings around to different places, setting off a treasure hunt to find what you used to be able to reach by pure muscle memory!