Measurement

Have you done a Spotlight search on the phone for Measure? Use Search on your iPhone, iPad, or iPod touch - Apple Support If you cannot find it, then see this for how to recover it. Delete built-in Apple apps on your iOS 12, iOS 13, or iPadOS device or Apple Watch - Apple Support

Unless you intentionally deleted it your phone has the Measure app. Go to the App Store and search for “the Measure app”. If the button says “Open” it is still on your phone somewhere. If it says “Get” tap that and reinstall it.