How to free up space

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

About iCloud, see the following Apple articles:

Sign in and use iCloud.com

Sign in and use iCloud.com – Apple Support (UK)

How to use iCloud on iPhone

How to use iCloud on iPhone – Apple Support (UK)

Manage your iCloud storage

Manage your iCloud storage - Apple Support

Check your iCloud storage online or on any device

Check your iCloud storage online or on any device – Apple Support (UK)

See also this Apple article: Upgrade to iCloud+

Upgrade to iCloud+ - Apple Support