Hello niranjan115,
Welcome to Apple Support Communities!
I understand from your post that you're trying to backup your phone to iCloud but it's telling you there isn't enough storage. I am happy to help.
It looks like your phone hasn't been backed up since June. It could be that you have accumulated more contents and data and that could be the reason why iCloud is saying you don't have enough space.
You can check and see what the next backup size is going to be and to see if you will or will not have enough iCloud storage to complete the backup.
To see the next backup size go to Settings > your name > iCloud > Manage Storage > Backup > Tap the iPhone you are currently using.
Here you will see Next Backup Size.
Let me know if that worked for you. If it is determined you do have enough space let me know and we'll go from there.
Have a great day!