Your 32gb is device storage, which includes your apps, messages, photos, etc. There is no way to expand your local storage. Think of it as a fused chip to your phone's logic board.
When you buy your iPhone, iPad, or iPod touch, it comes with a set storage capacity. The music you buy, the apps you download, the photos you take, and all of the other content that you enjoy on your device uses its storage. And depending on the size of your capacity and how much content you have, your device can fill up and run out of storage. When your device is full, you can’t increase its storage. But you can free up space.
In order to free up device storage, you will have to delete applications, files, photos, etc. You can move the data to iCloud and delete it from your phone. You can make storage space available on your iPhone, iPad, or iPod touch when you use iCloud Photos and turn on Optimize Storage. Or you can remove content from your apps—like photos, music, and Podcasts—or delete the apps that you're not using.
To see how much storage you have
- Go to Settings.
- Tap General.
- Tap [device] Storage.
You might see a list of recommendations for optimizing your device storage, followed by a list of installed apps and the amount of storage each one uses. Tap an app's name for more information about its storage.
If you're using iOS 10 or earlier, below Storage, tap Manage Storage to see which apps take up the most space.
the 50GB plan you bought is cloud storage.
You can use that storage space to back up your device and to keep all of your photos, videos, documents, and text messages securely stored and updated everywhere. Depending on the size of your backup and the amount of content you keep in iCloud, you might run out of free space. You can make room when you buy more iCloud storage or when you delete content.