Can my iPhone be wiped when I am connected to my employer's Exchange server?
Yes, depending on how things are configured, your employer may be able to wipe your device. The ability to wipe only the Exchange account data was added later as an optional wipe mode.

From another TechNet article:


  Your users carry sensitive corporate information in their pockets every day. If one of them loses their mobile phone, your data can end up in the hands of another person. If one of your users loses their mobile phone, you can use the Exchange admin center (EAC) or the Exchange Management Shell to wipe their phone clean of all corporate and user information. (emphasis added)


In other words, the phone is not "completely erased" -- but all user data is destroyed. I believe this is accomplished on iOS by throwing away the encryption key. The operating system remains, but all user data is gone.

For example:


  In June of 2016 Microsoft announced an update to the Exchange ActiveSync protocol which they called EAS 16.1. Among the improvements in EAS 16.1 was the addition of account-only remote wipes, which allows an administrator to issue a remote wipe for only the Exchange mailbox data on a mobile device. Previously, a remote wipe for an ActiveSync device would wipe the entire device if the user was using a native mail application to connect from the device.