Hi Mee474,
Storage can fluctuate if items in iCloud optimize to save space on the device. For example, when using iCloud Photos the photos are stored in iCloud and not on the device unless they are downloaded. You can view iCloud on a web browser to see what items may be saved there: iCloud
Additionally, it is also possible closing the Safari tabs helped to clear storage that has been used.
The following article offers additional details on managing the storage for your iPhone: How to check the storage on your iPhone and iPad - Apple Support
Use your device to check its storage
1. Go to Settings > General > [Device] Storage. You might see a list of recommendations for optimizing your device's storage, followed by a list of installed apps and the amount of storage each one uses.
2. Tap an app's name for more information about its storage. Cached data and temporary data might not be counted as usage.
Keeping your device up-to-date to ensure the latest fixes are installed. You can learn how to do that here: Update your iPhone or iPad - Apple Support
Let us know if those steps have helped.
Take care.