iphone 8 plus message app back button issue

I have a new iPhone 8 plus with iOS 11.1.1.

When I am done typing-sending my text message, I usually try to back up to the previous menu which is "Message", the list of all the latest senders and messages. I saw another post where someone asked about the "back button" and the reply was "there is no back button", so let me describe it this way: in the far upper left-hand corner, it looks like <#, where the # would be in a blue circle. That is the area I tap to get back to the main list. When I tap that area with my big fat thumb, sometimes nothing happens then I do it again, then all the messages fly by as if I am wanting to go to the very top of that discussion, then I tap it again and the main list of messages and senders shows up with a radio button by each sender, so i can select and delete them. None of this was what I needed or wanted. Conversely, when I have the phone on my desk and I try the same backing up routine with my skinnier index finger, it usually works out fine. Most of the time I am needing to text while standing or walking so my hand is holding the phone with the big-fat-thumb reaching high and left to move backwards and failing. I hope that someday the <# area can be bigger or smarter so I won't (mis) tap it so much. Or, if there is another way to go backwards, I am eager to learn.