I'm sorry about the issue. Unfortunately, there is no option to add more storage hardware to an iPhone, but you can free more storage space by doing the following steps:
1. Delete apps / games.
2. Remove videos / podcasts.
3. Remove pictures (transfer them to computer first if you need.)
4. Delete messages and/or set messages to automatically expire after certain days (in Settings > Messages > Keep Message.)
5. Turn off Photo streaming and sharing (in Settings->Photos & Camera->My Photo Steam & iCloud Photo Sharing)
- Also, here is a website link for video instructions:
Do you have any further question?
Please reply at the box below. Thank you.