my iphone 12 mini said my device storage was full. I have 10 GB of photos /videos on my phone, but I have 2 TB of icloud storage with only 741 GB used so far. Why doesn't my iphone put that 10 GB to icloud?

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. 

See -> What's the difference between device storage and iCloud storage?

What's the difference between device storage and iCloud storage? - Apple Support

See also the following Apple articles:

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