I spoke to Mitel about the whole external contacts/personal contacts in MiCollab Release 8+. I even raised a feature design request with them as we, as well as customers were becoming increasingly frustrated with the lack of ability to easily control/create your own personal contacts in the new MiCollab PC client, especially as the 7.3 client let you do this!!
Essentially they came back with an answer, you have the following options:
Sync with an existing AD server
Create an external LDAP server
Sync with outlook personal contacts
Sync with Windows 10 people app
Or.. use a work around by creating dummy users through MiCollab which link to external speedcalls
There is no way for users to control or create their own personal contacts in the new MiCollab PC client, or for the client to sync directly with the existing telephone directory on the MiVoice Business, which personally I find absurd as you can have a mixture of softphones and deskphones in the same business that arent able to see the same telephone directory, its a tough one to explain the reasons behind that when a customer asks..
Anyway, I was told something along the lines of.. thats how it is, live with it