Way to prevent the noise when 2 phones together
This phenomenon is called audio feedback which usually occurs when the sound from the speakers reaches back into the microphone, and then gets amplified because of the speaker-mic loop.

Common and general solutions are to cut off the loop, or at least reduce the loop gain by:


Wearing earphone or headphone (isolate the speaker and the mic, prevent the feedback loop completely)
Mute the mic when not needed to speak (prevent the chance of feedback loop)
Reduce the speaker volume (reduce the volume gain)
Take some distance between the speakers (reduce the volume gain)