If you are using a Samsung Galaxy S3, you should know that phone is a decade old. Whatever version of Android it is running is most likely outdated, defunct, and no longer supported. It would be no surprise if the Alexa app is not supported on whatever old version of Android the S3 uses. That means you won't be able to download or install the official Alexa app from Amazon. If you somehow manage to sideload it to your S3, it's probably not going to work anyway.