I am no longer able to access the Kanopy channel on my Roku-why is this?
I can view content only via my phone app linked to Roku.
It's still in the channel store. Whether it is supported or supported well, depends on its authors who are Kanopy (not Roku.)
That page has Roku right on their front page, so it seems they think it is supported.
Here's another page that might be useful:
https://help.kanopy.com/hc/en-us/articles/115004322594-Watching-Kanopy-on-Roku
That page includes "Kanopy will appear and play on any Roku device that is currently supported by Roku and receiving software updates."
What model of Roku do you have?
What kind of problem are you having? Sometimes the: remove the channel, reboot the Roku (don't skip this), (re)add the channel, process fixes problems.
I'm watching it right now, so it's still supported. Try @Strega suggestion of removing it, restarting your Roku, and adding it again.