edit server in iphone exchange email We used to use Mobile Iron to configure our users' Exchange email on their iPhones.

Recently it was decided to stop using Mobile Iron. I'm not sure how the rest of our IT dept managed the transition, made about a month ago.

Currently, an iPhone user's Exchange email server setting is incorrect, probably set to work with Mobile Iron.

Is the Exchange email server editable in the iPhone Mail app? 

I can't seem to edit it.
Generally speaking all exchange servers since (I believe) 2007 have an automatic configure function. So if your mail server is at mail.company.com the automatic configure URL will be autodiscover.company.com.

Assuming your mail server was set up correctly along with the correct DNS entries, merely removing and re-adding that account from your iPhone should fix the issue. Assuming your IT department hasn't done something non-standard.