Access on computer, but not phone. Getting error message.

Email is now up on computer, though all of my messages did not come through.  I get a daily email from something I belong to and did not get one today.  When I try to access on my phone I keep getting error message "Couldn't sign in".  I put the correct password in and this error message keeps popping up and then the alert for the error message is going off over and over again.