From my profile -> comments page, yes, and that's a regression -- it used to include a link back to the post's full comments feed.

But from the full comment feed for a post, I have options for upvote, reply, profile, and collapse to root.

Gotchya. I was tapping the root comment, and not a child comment. I'm surprised there isn't a "collapse" button when tapping the root comment.

Usually I don't reply or comment to HN on my phone, which is probably why I hadn't seen it before.