I just tried it in the version "Lineage OS Phone 19.0 (250000) " in the version from September 21 2018 - size 32 951 659 bytes
md5 8fdfeb93f527eb3…07c5
https://www.apkmirror.com/apk/lineageos/lineage-os-phone/lineage-os-phone-19-0-release/lineage-os-phone-19-0-android-apk-download/
instead of the preinstalled phone app. (I deactivated the preinstalled app)
So far it worked, I can accept calls, and I can make calls and the new dialer app is used as in-call UI. I can also use it to make calls or use the API to “ask to make a call” from OpenContacts
I have not tried yet if it also works after a device reboot. (Which was an issue with the replacement keyboard app)