Connection Issue for our VoiceEdge phone

Our office is using Business VoiceEdge phone for at least 2 years now.

Recently, some of my colleagues told me that there is a reception issue on our side during the phone call. 

When we make incoming or outgoing calls, the other person can hear us clearly, but we hear their voice intermittently. It was like the phone was on mute for a few second and back to normal again.

Could someone help to solve this issue? Thank you.