Icloud storage full issue

See the article Use the Files app on your iPhone, iPad, or iPod touch - Apple Support

Read the section - Use the Files app to manage your files on your iPhone, iPad, or iPod touch

When Mac and iPhone is signed in with same Apple ID and password on the same network in which iCloud Drive and desktops and documents box is turned as on , the documents can be searched from finder > iCloud > Documents ( use its spotlight ) to search them Narrow your search results on Mac - Apple Support

Read this article also Access and manage your files in iCloud Drive - Apple Support

And use get info ( right click on the document ) to see the size of document and delete it Delete files and folders on Mac - Apple Support

Follow the steps in the article.

Manage your iCloud storage - Apple Support

The iCloud data will be reduced and mirror in iPhone as well in iCloud.com see the article Check your iCloud storage online or on any device - Apple Support

Remove the device iPhone 11 from the web account ( see the section - Use the web to remove a device ) Check your Apple ID device list to see where you're signed in - Apple Support

May be you are using family sharing account Share iCloud+ with your family - Apple Support

Switch from your iCloud+ plan to your family plan

When you share iCloud+, any family members using the free 5GB plan are added to your family plan automatically.

If a family member is already paying for their own iCloud+ plan, they can choose to switch to your plan or keep their own and still remain part of the family. When they switch to the shared family plan, they get a refund for the remainder of their personal plan. They can't keep their current plan and use the shared family plan at the same time.

See Upgrade to iCloud+ - Apple Support

Hover your cursor on yellow bar it will show how much space is occupied by documents , delete more of them Mac keyboard shortcuts - Apple Support

You can see exactly what takes up space on your iPhone by going to Settings > [your name] > iCloud > Manage Storage. This will provide you with an overview of what is being stored in iCloud.