Future backup takes too much space

Hi!

My phone doesn’t backup my phone anymore so I did what everyone told : deleted photos, etc...

and when I went to see the size of the backup that wouldn’t start, it was a backup of 4,31Go?!

That’s really big since I have 5Go and it’s impossible to keep this much space.

I have an Iphone7 and I’ll gladly answers questions if you could help me, thank you!