How do I eliminate SMTP servers in the settings that I no longer use? Earlier today, I asked a question about SMTP server settings on my iPhone (iOS 11.2.5).  I've more or less figured that one out.  I realize that it doesn't really matter, but how do I get rid of all these extra SMTP entries that I no longer need?
From the same screen as your screenshot, click each of those smtp servers.  On the next screen at the bottom in red “delete server”.