If you really only have an email app on your work phone, and never log into it on that phone, then no, not unless you also told them your login and password for that account.
On the other hand, if you log into your account on that app on that phone, and have it remember your login info, then if they have access to your phone (either physically at any time, or remotely, via some remote access program), then they could open the app and use the saved login info to see your account.
If you log into your account on that phone, don’t have it remember your login info, and they have no other way to get your password, and if the email software doesn’t store a copy of your email on the phone, then I expect it’s very unlikely they will access your email.
Extremely unlikely, but IF they have and use some sort of recording software that can show them what your screen looked like while you were using it (unlikely that even if they had that, that they’d bother unless you’ve given them some reason to study all your activity) OR if the email app doesn’t encrypt your email traffic, and they have a network sniffer that records all traffic on their local network, then it’s theoretically possible they could discover your communications there. But that seems to me really unlikely unless they have very strong security and are for some reason bothering to try to spy on all communications. That’s not likely at all unless you’re working for the military, CIA, hyper-paranoid gits, or something.