why do i have 2 phones in my icloud backup? How can I remain 1 folder backup?

Currently, I am switching my data from my old phone to a new phone (same provider), but there are 2 backup folders. My storage is full, there are 2 backups one is an old phone back up the other is a new phone backup. The new phone backup is not complete, the reason of storage is full. If I delete the old phone backup will all my data in my current new phone be lost? Or the data still will remain in my new phone after deleting the old backup folder from there I can do my backup again to the new phone data folder?