I’m having a similar issue with my device, which is the Video Doorbell 2 too, after installing it today. The sound you hear at the doorbell from the phone is clear but the volume on the phone is either really low or you can’t hear them at all but you can see their mouth moving. I know that sound is enable as I’m able to hear them if they talk loud but it is still feint. My phone is an iPhone X on iOS 13.5.1 with Ring app version 5.27.1