Michelle Phillips stepmother of Mackenzie Phillips, denied allegations of Mackenzie due to her mental illness. According to her, Mackenzie has been arrested in drug related cases and has been to Celebrity Rehab. There was also a time when she called her (Michelle) telling about this 'incest relationship' they have had with her father and called back again and told that it was joke.
In my opinion, Mackenzie is telling the truth. In fact, Chynna Phillips half-sister of Mackenzie, back her up . Here's some interview with Chynna from LA times.
She tells Us that in 1997, 11years after MacKenzie says the affair ended, Mackenzie called Chynna and told her about the physical relationship.
"Was he actually raping her? I don't know," says Chynna. "Do I believe that they had an incestuous relationship and that it went on for 10 years? Yes."
I think that would be enough.
Know more about Michelle and Chynna Phillips.