iPhone not backed up due to full iCloud storage

When I click on settings in my phone, I get messages that says: Apple Account Suggestions, and then underneath that it says: iPhone not backed up. Now when I click on iCloud storage, it then tells me that, my iCloud storage is full and it may not have had enough space for my last backup to happen. No one says that your iCloud storage is full. I know that includes photos but does that also include apps? And what else? And now, I guess my question is, without upgrading to iCloud+ for more space, what would my next option be? Because down below that the button that says, back up now is blue which means it looks like I can click on back up now. The back u now button is not ‘grayed out’ where you can’t click on it. If that makes sense.

[Re-Titled by Moderator]

Original Title: iPhone not backed up