Earlier quoted context omitted.
I don't know if Verizon is actively doing it, but since most providers that offer DoH have well-known IPs, like 8.8.8.8, 1.1.1.1, 9.9.9.9, they could easily just block traffic heading in that direction.
This follows along with what I read, at first it’s easy to block but it’s a losing proposition because anyone can stand up a doh server (which is also a network security nightmare)
Blocking popular DNS providers is a common tactic deployed by ISPs. It is technically easy enough to bypass depending on your skill level and interest in doing so. Their strategy is make it difficult for majority of their users, who won't know or care, users doing all this will not make substantial impact on revenue generated from selling this data, or from showing adds etc so they don't make the effort.
DoT/DoH is not going to change this, Firefox's market share is not enough for that. I don't see Chrome or Safari implementing this functionality at all.