Small gray button on iPhone screen

Could anyone please tell me what this little gray button is on my iPhone screen. It expands out to this, screenshot attached. It would not screenshot a picture of the little gray button. Could someone tell me what it is, how it suddenly got on my phone after a year, and most importantly, how do I get rid of it. I do not want it, and it is always in the way of something else, no matter where I put it. Thank you for your assistance.