To manage mobile devices that have already been configured to connect to an Exchange account, log in to OWA. In OWA, locate the Options button on the upper-right corner and click, followed by See All Options. Next, along the left-side menu, click Phone.
You should now see a list of all the phone devices that have been configured for this Exchange account. For more information, click the Help link (the question mark icon) on the upper-right corner of the page in OWA.