It will work (with possible issues) if you set up your network like this:
NTD===>NF3ADV(LAN port)===>(WAN port)TG797===>home phone
If the NF3ADV has an option called 'SIP Passthrough' or 'SIP ALG" (usually under the WAN settings somewhere) make sure it is disabled otherwise you may not be able to receive calls.
As suggested, disable WiFi on the TG797 and maybe DHCP - just be aware that if you disable DHCP you will not longer be able to access the TG797's settings page in your browser.
NTD===>NF3ADV(LAN port)===>(WAN port)TG797===>home phone
If the NF3ADV has an option called 'SIP Passthrough' or 'SIP ALG" (usually under the WAN settings somewhere) make sure it is disabled otherwise you may not be able to receive calls.
As suggested, disable WiFi on the TG797 and maybe DHCP - just be aware that if you disable DHCP you will not longer be able to access the TG797's settings page in your browser.