Hi Ellen,

Give this method a try;

In the case of a shared-line appearance, Remove From Device removes the directory number on the current device only and does not affect other devices.

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a0080739bb8.html

Removing a Directory Number from a Phone

Perform the following procedure to remove a directory number (DN) from a specific phone.

Procedure

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Step 1 Choose Device > Phone.

The Find and List Phones window displays.

Step 2 To locate a specific phone, enter the search criteria and click Find.

A list of phones that match the search criteria displays.

Step 3 Choose the device name that contains the directory number that you want to remove.

The Phone Configuration window displays.

Step 4 In the Association Information area on the left, choose the line that you want to remove.

The Directory Number Configuration window displays.

Step 5 In the Associated Devices pane, choose the device name of the phone from which you want to remove this directory number.

Step 6 Click the down arrow below the Associated Devices pane.

The phone name moves to the Dissociate Devices pane.

Step 7 Click the Save button at the bottom of the Directory Number Configuration window.

The Phone Configuration window displays with the directory number removed. The change gets automatically applied to the phone; however, you can click Reset Phone.

From this doc;

Directory Number Configuration Overview section in the Cisco Unified CallManager Administration Guide, Release 5.0(4).

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a00806b17c6.html#wp1121142

Hope this helps!

Rob