ORBI CBK752 drops VOIP calls every few minutes

What Firmware version is currently loaded?
What is the Mfr and model# of the Internet Service Providers modem/ONT the NG router is connected too?
Does this happen with only wireless connections or does it happend on wired connections as well? 

What is the size of your home? Sq Ft?
What is the distance between the router and 📡 satellite(s)? 30 feet or more is recommended in between RBR and RBS📡 to begin with depending upon building materials when wirelessly connected.
https://kb.netgear.com/31029/Where-should-I-place-my-Orbi-satellite 📡

What channels are you using? Auto? Try setting manual channel 1, 6 or 11 on 2.4Ghz and 40 to 48 channel on 5Ghz.
Any Wifi Neighbors near by? If so, how many?

Try disabling the following and see:
Armor, Traffic Meter ,IPv6 and Set 20/40Mhz Coexistence to 40Mhz only. Set CTS to 2347. Set Short preamble instead of Long preamble modes. Save settings and reboot the router and satellite(s). Under Advanced Tab/Advanced Settings/Wireless Settings

You can find other speed diagnosis steps in the community faq: https://community.netgear.com/t5/Orbi-AX/Community-FAQ-My-Orbi-speeds-are-slow-inconsistent-and-don-t-my/m-p/1982974/highlight/true#M7849

One User Experience/Configuration:
https://community.netgear.com/t5/Orbi-AX/RBK753S-update-Rock-solid-in-terms-of-speed-and-stability-since/td-p/2095781/jump-to/first-unread-message