What should my settings be to improve my wifi VoIP connection (QoS settings possibly)?

Model:  C6900 AC1900 Cable Modem Gateway (NOT the C7000)

IP:  Comcast Pro (100 mbps)

I'm using the Obihai1062 VoIP phone with google voice, which is connected to the C6900 Gateway via the 5G wifi connection.  Call quaility on my end is excellent (HD telephone) however callers report i'm choppy or they can't hear me from time to time.  Open to suggestions on how to improve the VoIP connections. I'd perfer not to connect the phone via CAT5/7 cable to gateway if possible.  I'm actually hoping to add another Obi1062 phone that connects via wifi as well.  

My wifi setting are still as out of the box with the exception of adding a password, changing the broadcast name and activating the guest network. 

I understand the QoS settings may improve the VoIP quaility.  If so, what should I change?   

All of this is within a 600 sqft space. 

Current network connections include: 

1x smart lighting hub (via CAT 5 to 1/4 LAN ports)

1x Sonos hub (via CAT 5 to 2/4 LAN ports)

2x iPhone (wireless via 5G)

2x cameras (wireless via 2.4)

1x iPad (wireless via 5G)

2x Sonos speakers (via wifi 2.4)

2x Smart DVD players (via wireless 2.4)

1x Smart TV (via wirless 2.4)

2x Desktop PC (wireless via 5G)

1x Printer ((wireless via 2.4G)