Thanks for reaching out to Apple Support Communities, sanghmitra113.
We understand you're wanting to upload your photos to iCloud to help free up space on your device. First, it is important to note that photos you back up to iCloud use both iCloud Storage as well as device storage so it's possible that they are not backing up because your iPhone storage is too full. If that is the case, the steps in the article below in the "Make sure that you have enough storage" section will help walk you through freeing up additional space so those photos can start backing up with iCloud.
Set up and use iCloud Photos
However, if you're being prompted to purchase additional iCloud storage, it is possible that the 200GB storage plan is not enough to backup all of your photos and you may need the 2TB in order to store all of them in iCloud. You can check how much storage your photos are taking up in your iPhone settings by following the steps in the link below. This may give you a better idea of how much iCloud storage you will need to back them up.
How to check the storage on your iPhone, iPad, and iPod touch
We hope this helps!
