I tested and did not experience such thing. This account I am using is an ordinary account with no special privileges (just to experience what others experience).
What I can say is that when you are on mobile or on your profile, you can see a box, just ordinary text area, it is when you focus on it that you will then see the err comment button.
The functionality of the site on desktop and mobile is the same, just layout that is different. You can even toggle the layout by using the Toggle Layout link (on the footer on mobile or sidebar on desktop).