Here’s how the response post looks in my browser (using Firefox on a desktop). Notice in the top left corner of the screengrab, that arrow and your icon: That shows that this post is a reply addressed to you.
I’ve never used this site with my phone. It might behave differently.
It won’t do it if you’re replying to the post immediately before yours. So I’ll get it for this post (it will show your avatar in top right because @MrGreenJeans reply is between us), but if you reply to me immediately after my post, it doesn’t register as a reply or send a notification.