1.
Try to free up iPhone device storage see this Apple articles below:
If you need more space for an update on your iPhone, iPad, or iPod touch
If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support
How to check the storage on your iPhone, iPad and iPod touch
How to check the storage on your iPhone, iPad and iPod touch – Apple Support (UK)
Clear Other storage on your iPhone or iPad
Clear Other storage on your iPhone or iPad - Apple Support
-> What's the difference between device storage and iCloud storage?
What's the difference between device storage and iCloud storage? - Apple Support
2.
iCloud storage:
Check -> Go to -> Settings -> your name -> iCloud -> if you see 50 GB (or 200 GB or 2 TB) then you have an iCloud subscription.
If you have an iCloud subscription, you will receive a monthly bill from Apple, check your email box.
You pay monthly for iCloud storage.
How to use iCloud on iPhone
How to use iCloud on iPhone – Apple Support (UK)
See the following Apple articles:
Get help with iCloud Photos
Get help with iCloud Photos - Apple Support
Set up and use iCloud Photos
Set up and use iCloud Photos - Apple Support (IN)
Access and view iCloud Photos on your iPhone, iPad or iPod touch
Access and view iCloud Photos on your iPhone, iPad or iPod touch – Apple Support (UK)