Sync issues between SBS 2011 Exchange and iPhone

We have a SBS 2011 server using Exchange 2010.  We have several users that have their emails syncing on their iPhones.  I am having issues with one user getting their emails to work on their iPhone.  I have tried to configure this user on my iPhone with the same results.  We both are using iOS 11.4.1.  Everything is configured correctly and I get all check marks after manually configuring the mail server in Accounts & Passwords.  But when I go to the Apple mail app it comes up with the message "Cannot Get Mail  The connection to the server failed."  I'm thinking it is a problem with this particular user because everyone else that I have on iPhones is not having this issue.  Any ideas or suggestions would be greatly appreciated.