Not Fantasy Question! How do I sign in on my iPhone?

I am logged in somehow on my computer but I can never log in on my iPhone. I put in my username, TheFreakFreeman, I put in my password, and it gives me three chances. Idk how I ever got logged in on the computer because it took a long time and I have not signed out. This is quite frustrating because the only time I can get on here is at work. Did anyone else have a hard time logging in originally? If so, how did you fix it?
Been a member for a week now.