Deleting backup from old iphone, on new iphone

Backups are not stored on an iPhone. They are stored either in iCloud or in iTunes on your computer. So deleting a previous backup is done in one of the two places mentioned above.

Once you set up a new iPhone, that new iPhone's data is on the iPhone, not in a backup somewhere

iTunes & iCloud keep separate backups per device. Deleting one device's backup has no affect on the data or backup of the other device/devices.

I have set up my new iphone but when i try to back it up on icloud it is saying i don't have enough storage. When i go into manage storage I have two old back ups from my last iphone. When i try to delete the oldest backup to free up space it asks me 'do you want to turn off backup and delete all backup data for my phone from icloud?' If i select 'Turn off & delete' does this only relate to this particular backup or am I going to lose everything on my icloud backup i.e. my most recent backup a few days ago???