OpenDNS is a service to be used in networks you own, not for your devices in other networks. It seems another OpenDNS user was successful with registering the shared public IP address of this phone hotspot which he shouldn't have been doing. Best is to raise a support ticket, link "Submit a request" above, to report this shared IP address to OpenDNS staff. They will add it to the list of addresses not to be registered with OpenDNS.
"will I have to switch to Google DNS nameservers?"
Why Google's? There are better DNS services. But yes, every recursive DNS service not coming with any filtering capabilities based on your IP address would be fine for your purpose.