How do I backup photos to iOS Google Photos without duplicating photos on iPhone

My photos have synced to my Google account using the iOS Google Photos app. Each photo is now taking twice the storage on my phone: the iOS Photos app **and** the Google Photos app. Inside Google Photos there is an option to remove the uploaded photos from the iOS Photos app but I don't want that. I want to remove the photos from Google Photos but I still want to be able to view the photos in the Google Photos app that were uploaded to my Google account. Basically, I want to back up my photos to Google Photos but I don't want the Google Photos app to duplicate my pictures on my phone.