Uploading your iCloud photos to your Google Photos on an iPhone is easy. The only concern is, that you need to have enough free space on your phone. This is because when your iPhone uploads to Google Photos, it will be drawing from your iPhone's local storage, not iCloud, so you'll want the highest-quality versions of your photos on your device.
Here's how you can upload iCloud photos to Google Photos on iPhone:
- In Settings, select Photos & Camera.
- Enable "Download and Keep Originals" if it's not already checked enabled. You may need to wait for this process to complete.
- Download Google Photos on your iPhone.
- Open Google Photos, and during setup, make sure Backup & sync is set to On. Now, your photos downloaded from iCloud will start uploading to Google Photos.