Can I buy more gbs for my phone. I don’t have any storage left.

No you cannot buy more storage for your phone. It will always have the amount it came with. You can buy space in iCloud, Apple's synching service. See this link...

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

The only way you can gain space is to delete photos, messages, apps, etc.. Be sure to save important photos and data to your computer or an external drive. this video may help...

you cannot expand the capacity of an iPhone

you may be able to use iCloud storage to help..

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

Sorry, but it is not possible to add storage space to an iPhone.

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Just so happens, 2 of us responded within a minute of your post

Please read the links you have been given. Click on the blue links...