DIAGNOSIS This is almost always a Wi-Fi bandwidth or signal strength issue at the camera, not your phone.
FIX Check the camera's RSSI (signal strength) in Device Health in the Ring app. If it's below -65, the signal is poor. Move your router closer, use a Wi-Fi extender, or relocate the camera. Ensure it's on 2.4GHz for better range.
IF THAT DIDN'T WORK Other devices are hogging bandwidth. If someone is streaming or downloading on your network, it can choke the camera's video stream. Try a live view when other high-bandwidth activity is paused.
HEADS UP The Gen 2 Indoor Cam doesn't support 5GHz as reliably for live streaming. Sticking to 2.4GHz is the most stable fix for lag.