I would like to update my phone storage

There is no way to upgrade your phone's storage. It will always have the same amount it came with. You can buy space on Apple's synching service iCloud. The only way to create more space is to delete photos , messages, apps, etc. Be sure to save important photos and data to your computer or an external drive. Check this link...

What's the difference between device storage and iCloud storage? - Apple Support

This video may also help...

https://www.youtube.com/watch?v=bnhuHSv_WrI