This was not a one-night thing - Mike Johnson of PWInsider has reported that Phillips is replacing Joseph on the Raw brand going forward, with the Rumble marking the switch.
The report notes that Joseph is still with WWE, and that the decision to make the change was made last week.
Joseph's future role with WWE is to be determined.
Joseph took over as lead Raw announcer from Michael Cole on September 30, as part of a trio that included Lawler and Dio Maddin. Previously, he provided commentary on 205 Live and NXT UK.
Phillips provided lead commentary duties on SmackDown for periods in 2015, and consistently from the spring of 2017 through this past September, after which Cole replaced him upon SmackDown's move to Friday nights on the FOX network.