If you haven’t tried it before, posting embedded links in Discourse on an Android phone is a major pain in the ass. You highlight the text, and the cut/copy/paste dialogue pops up and covers the link button. You have to do pinch-zooms until you reach a level of magnification where the button peeks from the edge of the pop-up, then pinch back down to regular size to post.
I recently discovered, though, if you just highlight the text you want to link from (and have the URL on your clipboard) you can simply paste and it will do the embed properly instead of replacing one text with the other like a standard highlight/paste would.