Yes and no but most likely no. You don't have to have the phone in your possession but here is what Apple says must happen to backup automatically:
Automatically back up with iCloud Backup
Make sure that iCloud Backup is turned on in Settings > [your name] > iCloud > iCloud Backup.
Connect your device to a power source.
Connect your device to a Wi-Fi network.
Make sure that your device's screen is locked.
The problem for you is that the phone is most likely not connected to a power source and likely not to a Wi-Fi network.