Seems like they changed repository URL. Early I had

maven {url "https://linphone.org/releases/maven_repository/"}

in build.gradle project-level file and faced the same issue.

Now I have replaced it with

maven {url "https://download.linphone.org/releases/maven_repository/"}

Found this in their commit on github: https://github.com/BelledonneCommunications/linphone-android/commit/c4eb74ff0dc25a9476eb71113059b2f7599183eb

Now project builds fine.