How do I block spam text via Verizon messenger service on a Pixel?
If you mean Messages+, that app is for all practical purposes dead at this point because Verizon is completely shutting it down in a few more weeks. I'd switch to Google Messages, where blocking a text sender is relatively easy:
https://support.google.com/messages/answer/7029021?hl=en&co=GENIE.Platform%3DAndroid
You should not be using Verizon Message+ on a Pixel. Use the stock Android Messages app (blue & white app icon). As mentioned above it's very easy to block a number within Messages.
We're sorry to read about the issue with spam messages. Is spam protection on in the Settings in Messages app? ~Peter