Hello id like to buy more storage on my phone but i cant can you help me?

You cannot add storage space to your iPhone. You can delete unused items or purchase a phone with more space.

See this Apple articles below:

Clear Other storage on your iPhone or iPad

https://support.apple.com/en-us/HT211686

If you need more space for an update on your iPhone, iPad, or iPod touch

https://support.apple.com/en-us/HT203097

What's the difference between device storage and iCloud storage?

https://support.apple.com/en-us/HT206504

What does iCloud back up?

https://support.apple.com/en-us/HT207428

Sorry no. The internal storage on iOS devices cannot be incremented.

Regards

Giulio