Key hash is based on the computer you use to build the APK, it is not dependent on what phone it is run on. So, if you only work on your app from one development machine then there is only one key hash you have to worry about for your app. Currently, you are using an android debug key when you are still developing your app, when you want to publish to Google Play, Google requires you to sign the APK with your own key, and not the android debug key. When you create your own key to sign your APK, you need to also copy and paste the key hash of your own key in the app settings on Facebook.