Hi,
As far as I know, there's
no such feature in Exchange server to "hide" email folders on phone.
However, the Exchange administrator or end user remain allow to manage activesync device if it lost, stolen or other compromised.
We can disable those missing device by end user, or
remote wipe as Ed mentioned above.
By the way, we can configure a
mobile device policy to improve mobile security, for example:
PasswordRequired,
Password expiration,
wipe a device after a specific number of failed password attempts.

More details, refer to:
Mobile device mailbox policies.
Regards,
Allen Wang
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