I’m not sure what material or style these steps are, but they’ve started crumbling after water got into a crack and froze during the winter. It seems to be getting worse and I’m wondering how to address it. Is this something that can be patched or do I need to remove all this material and start over?
Call a masonry person and get their quote and ask what they would do to fix. Even if you want to diy it, you'll be able to find out some reccs, and if the price is right, you might want to save a headache and hire them.
Yeah looks like a "remove it all and redo it".
I'm not a specialist though so a pro from your region is probably what you should listen to.