Hi @charlesh.wvit6j and welcome to the Community!
I’m afraid there is no way to extend the number of rings before a call is sent to voicemail. Republic has already set it for the maximum length of 30 seconds (typically 5-6 rings).
Do you know how many times your phone rings before the call goes to voicemail? Might it be a matter of simply not hearing the fist 2-3 rings? As a test, if you call your Republic phone from another phone how many times do you hear it ring before going to voicemail?
I ask because Motorola phones have a “feature” known as an ascending ringtone. Long story short that means the volume of the later rings is higher than earlier rings.