In ARS Dialled Digits you will find Digits matching International e.g. 9011 + Unknown, 901X + Unknown, 90 + Unknown
These should all terminate to 1 route
Make sure none of your other dial strings match that route
Check the Route for above and make note of what restricted COR group applies. Again, make sure no other route chares the same COR group.
Check the restricted COR group Members. Hopefully, your Admin phones have a unique COR assignment separate from the rooms. If not, they will have to be.
Add the Admin phones COR to the Restricted COR group for International dialing and Bob's your Uncle.
FYI, I'm being purposefully vague. If you cannot follow that and understand the purpose, you have no business messing with it.
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What's most important is that you realise ... There is no spoon.