If you don't want them to auto upload, you have to turn off that option, otherwise it will continue to happen.
If you are using the "Google Photos" App, open the app and then tap "Menu". Next tap "Settings" and then "Backup & Sync". On the next screen move the slider over so you are no longer backing up and syncing the photos on the phone to the photos on Google.
Once this is done, anything you delete from the google account, should not reappear. However, it should still be on the phone.
NOTE: You may want to consider backing up all the photos to say a computer though, as if they won't be backed up to Google, then you will lose them should you lose the phone, it breaks, is stolen, etc.