That's not an option with personal directories; they are always editable by the end user account. You can use ecosystem partner products (or your own coding if you're so inclined) to create read-only directories and then subscribe these to the phone(s) that you want to see that custom set of listings.
To be honest, at very small scale you could just write the XML flat file in accordance with the XML SDK, create a phone service with the URL to that XML file, and subscribe a single phone to it. Anything more ellaborate than this just makes it easier to maintain at scale.
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