Hi again keseindrei!
For your situation, it sounds like the storage being low on the iPhone may be the concern. If the Photos status is saying that you do not have enough storage, you would want to delete enough apps or data to allow the Photos to download in. You mentioned 30.9 GB of 32 GB, is that storage available or storage used? You can review the steps of where to check this at the article below.
How to check the storage on your iPhone, iPad, and iPod touch
The phone will need to have enough space available to store the full resolution photos, but will be able to be optimized for storage once the download is finished. You can enable the setting 'Optimize iPhone Storage', which will help the Photos take up less space on the iPhone over time. The article below explains further how your iPhone and iCloud storage work together to manage your Photo library.
Manage your photo and video storage
As the above article explains, "With Optimize Storage, smaller, space-saving photos and videos are kept on your device while all of your original, full-resolution versions are stored in iCloud"
Keep in mind you should be able to download these apps back in once everything is settled. The Photos require more space at first, but will reduce in size over time with the Optimize iPhone Storage setting mentioned earlier.
I hope this answers your questions! It sounds like you do not need to upgrade your iCloud storage further but may still need to free up some space on your iPhone. Apple Support would certainly be able to work with you further on this individually, don't hesitate to start a case with them if needed!
Contact Apple Support
Have a great day!