Support for dialing phone numbers from contacts is handled in the Configure dialog, choosing a program such as Ekiga or Skype. With KDE Connect's tel:// URL handler, most programs on my system can tell my phone to dial a number this way without extra configuration, including Firefox and Okular. KAddressBook is an exception, because it seems to require its own configuration for setting how to dial a number instead of using the mechanism these other programs utilize.
Yes, would be nice to have Kaddressbook better integrated with KDE Connect. Among the actual options in the contact options, in Kaddressbook's actions (the first section, I don't know if it is "Contact options" exactly in english) regarding the phone numbers, besides ekiga ans Skype a new option "Dial via KDE Connect" or just "KDE Connect" would be a plus. The simple command "kdeconnect-handler tel:%n" does the trick and sends the number in question to your phone's dial app just like when you click a tel:// link in Firefox.
(In reply to eemantsal from comment #1) > Yes, would be nice to have Kaddressbook better integrated with KDE Connect. > Among the actual options in the contact options, in Kaddressbook's actions > (the first section, I don't know if it is "Contact options" exactly in > english) regarding the phone numbers, besides ekiga ans Skype a new option > "Dial via KDE Connect" or just "KDE Connect" would be a plus. The simple > command "kdeconnect-handler tel:%n" does the trick and sends the number in > question to your phone's dial app just like when you click a tel:// link in > Firefox. Sorry, "present" no "actual options".