Does the limited warranty under the iPhone cover back glass repairs?

No, the warranty does not cover user damage, it covers manufacturers defects.

IMPORTANT RESTRICTION FOR iPHONE, iPAD, APPLE TV AND HOMEPOD SERVICE.

Apple may restrict warranty service for iPhone, iPad, Apple TV and HomePod to the country where Apple or its Authorized Distributors originally sold the device.

Service & Support. Apple Authorised Service Providers and Online Support. Explore Service Locations. 

Find Locations - Apple