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
2.
What's the difference between device storage and iCloud storage?
What's the difference between device storage and iCloud storage? - Apple Support
See this Apple article: Upgrade to iCloud+ -< Upgrade to iCloud+ - Apple Support
See also: iCloud+ plans and pricing -> iCloud+ plans and pricing - Apple Support
Manage your iCloud storage
Manage your iCloud storage - Apple Support
3.
You need to have a good Service & Wi-Fi.
If they are On, turn Off Hotspot & VPN.
Charge the battery > 70%.
If you can't connect to the App Store, iTunes Store, or other Apple services
If you can't connect to the App Store, iTunes Store, or other Apple services - Apple Support
-> If you tried all of the above steps and you still can’t connect, contact Apple Support.
