have backed up photos to icloud but iphone storage hasn’t freed up

No. You may be able to reduce the size of your library on device by optimizing photos (settings - photos). Originals are then kept in iCloud with lower-res images on device. This can save substantial space. iCloud synchronizes so if you delete or add an image it deletes or adds across all of your devices and in iCloud.

What might “backed up photos to i[C]loud” mean exactly?

• What device was this done from?
  • Model
  • Operating system version
• What steps were performed?
• What responses were seen?
• What steps made you think iPhone storage was freed?
• etc.