When your Mobile phone is enrolled, you are able to sync all your work contacts onto your phone.
You can choose to turn this off and on, and manage the accounts you would like to sync your contacts from.
1. Open up the Settings app on your iPhone and select Passwords and Accounts
2. Select the correct Email account under Accounts
3. Toggle Contacts on or off
You can also manage the accounts you choose to sync from in the Contacts App
1. Select Groups in the top left
2. Select the account. A ✓ (tick) means the contacts are syncing for that account. Select again to remove this