azrobert,
Thanks for the tip. When I plugged my 2 line phone handset into the Obi 202 phone port 2, and called my "line 1" (Anveo, SP3) number, line 1 (only) on the 2 line handset rang. This means that the Obi was applying ringing voltage to the inner pair of phone port 2 incorrectly.
After changing back to Obi 202 phone port 1, I then tried your tip of using the Obi expert tool and changing SP4 (Anveo 911) X_InboundCallRoute (which had been {ph1,ph2}) to {} as you suggested; this resulted in inbound calls to "line 1" (Anveo, SP3) not ringing at all, but going straight to voicemail.
I then tried changing SP4 X_InboundCallRoute to {ph1}. This now seems to have Anveo SP3 ringing only on line 1 of my handset and RingTo SP2 ringing only on line 2 of my handset AS THEY SHOULD. Your "hunch" that Anveo was "commingling" or somehow bridging the settings for their 911 service SP4 (required for RingTo) and their basic service SP3 was correct; the result was having both phone lines ringing when only line 1 was called.
Thanks so much to you and all the others who contributed to solving this problem.