Include phone frame in snapshot in Android Emulator
If you want to use the emulator without Android Studio, you can use this web tool by google to add device frames to the screenshots:
https://developer.android.com/distribute/marketing-tools/device-art-generator
By design, the Android Emulator just takes the full resolution of the app screen. If you want the device screen, take the screenshot from Android Studio. See this page: https://developer.android.com/studio/debug/am-screenshot.html
Inside of Android Studio, you can add and remove the screen, screen glare, and some additional cropping options.