Feedback can be caused when sounds loop through multiple microphones. To overcome feedback, users who aren’t speaking can mute their microphones. Alternatively, everyone can wear headphones.
Phone.com Video Conferencing uses an Acoustic Echo Cancellation (AEC) process that should cancel echoes created by your own computer when you are not using a headset, but they may be audible to other participants. The AEC process can fail when using two audio devices, for example an internal speaker and an external microphone, or if using the computer audio while also using the phone to dial into the conference audio.