Dirk,
There is an idea here for this functionality, so I suggest you review it and vote!
The main issue, however (I believe) is that Genesys doesn't have an "phone book" or "speed dial" feature. External Contacts are actually meant to act as a form of "mini-CRM", but many, many sites use them to create external phone books and face issues like this. This is another feature (out of many!) that PureConnect has, but Genesys Cloud doesn't, all of which which really need to be addressed if Genesys hope to not lose customers when PureConnect finally reaches EOL.
HTH
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Paul Simpson
Eventus Solutions Group
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