A Microsoft file hosting and synchronization service.
Hi! Luke C777,
Welcome to the Microsoft Community!
I realize that you want to know if deleting photos from OneDrive will cause photos to be deleted from your phone and I understand how you feel.
In fact, it will depend on the brand of your phone.Currently when using the OneDrive app to upload files in phones other than Samsung phones, it is a one-way sync.So deleting photos from OneDrive will have no effect on your phone's photos.
However, if you are using a Samsung phone and have the link between Samsung Gallery and OneDrive turned on, then when you delete the photos in OneDrive, the photos in your Samsung Gallery will also be deleted. Finally I would like to explain to you that when we delete photos from OneDrive, the photos will be in the Recycle Bin, and you can restore them through the Recycle Bin without deleting the photos in the OneDrive Recycle Bin. So I suggest you to make sure that the content in your phone is not affected after deleting the photos before deleting the content in OneDrive Recycle Bin.Feel free to post back if you need further assistance.Thank you for your understanding and patience.Best RegardsEddy | Microsoft Community Support Specialist