The reason for the echo is the microphone replaying the sound from the speakers.
It is recommended to use a headset or headphones to avoid it.
Your cell phone will also make your speakers buzz.
If there is the same conference participant in the same room with you, the problem may repeat.
Use a headset or headphones. Make sure there is no participants in the same room as you in your conference, recommend that they also use a headset or headphones if they are around.