According to reports, it seems that in the latest version of Google Photos, it will now inform users and give them the option of syncing their deleted photos. As you can see in the prompt above, deleting a photo on your phone will prompt whether or not you want to remove it from Google Photos as well.
This is a good idea especially if you use third-party gallery apps where it might not be synced with Google Photos, so this prompt will help you keep your photos synced even if you use other apps to browse and manage your photos. It is also a good idea because sometimes you just want to clear space from your phone but not necessarily want it to be deleted from the cloud.
The update and feature should already be live if you are using version 1.23 of the app, so if you haven’t updated your app already, you should probably go ahead and do so.