Connectivity/Digium Phones/Phonebooks seems to be the one systemwide phonebook accessable from Digium phones.
Unlike Sangoma’s Contact Manager, it can not be edited in the UCP (correct me if I’m wrong).
The data appears to be stored in /var/www/html/digium_phones/contacts.xml. That file gets overwriten on each “Apply config” though.
Who or what is writing that XML-file?