High latency phone web browser when viewing stream from ffmpeg but seem fine on pc

stream video to a room by ffmpeg. The video seems very good on web broader desktop, but almost dead on phone browser. even stream produced by another phone or desktop seems to be slow and bluey. However this is the same when using browser to browser using a computer.

is this expected outcome on a phone browser?

Do I always need to send rtcp + rtp? why not sending rtp only

Any idea why the video call on the demo or any application perform very poorly on phone more than desktop even both devices connects to same Wi-Fi.