On the bottom left-hand corner of my mail on my iPhone as a circle with three lines through it what is that?

That is the filter button. Default, if you tap it, is to filter by "unread". You can select the option bar at the bottom and change it to "flagged" , or "addressed"

Suspence02 wrote:

What is the circle with the three lines in it on the bottom left-hand corner of my mail in my iPhone

Just tried in on my Yahoo and Exchange account, when you click on it, it shows you the unread emails.