For the readership who searched for an answer…
I'm assuming the 2 tiered failover setup failed, due to not isolating individual external DNS I.P.s with specific gateways, on System: General Setup https://pfsense/system.php. I'm not sure why that is necessary, and why only one DNS server is available to each gateway, in such a configuration. If a server is down, or unreachable, I'd much rather have a list. I wonder what would happen if each individual D.N.S. I.P. was an alias I.P., pointing to a list, shared by all gateways…
I gained insight on that issue, by trying to help someone on here. Doing so prompted me to re-read THIS: https://doc.pfsense.org/index.php/Multi-WAN_2.0
The remaining problem had been that the gateway selected, was the tethered phone, with no defined route through the OpenWRT box's gateway.
I changed the gateway to the OpenWRT box, and am back online via pfSense.
I'll have to wait to try a failover setup, but the main problem is SOLVED.
Of course you should always check the simple things. True, none of us like to jump through a phone tree, to get a clueless Customer (dis)Service "tech", reading script prompts like, "Is your device turned on?" However, it can be VERY helpful to have someone double check, especially someone with far more experience.
"Thanks"… :(