Phillips is the half-sister of Mackenzie Phillips, whose claims last fall about a sexual relationship with their father put the family into crisis.
"After much thoughtful deliberation Chynna Phillips has checked herself into an undisclosed treatment facility for anxiety," Grubman says in a statement. "With the full support of her family and friends, she is looking forward to her recovery. We ask that people respect her and her family's privacy at this time."
Phillips, 42, is married to Gossip Girl star Billy Baldwin, and they have three children.
Mackenzie’s bombshell revelations were difficult for Phillips to handle, says a source close to Phillips. But she checked into rehab for a number of reasons, not just her half-sister’s allegations about their father. “It’s a combination of things,” says the source. “She hasn’t been the same since the summer.”
Another source says Phillips is in rehab to deal with stresses in her life “and not drugs or alcohol. Not at all.”
She came forward on The Oprah Winfrey Show to support her half-sister, who made headlines with her revelations their father, "Papa" John Phillips, raped Mackenzie when she was 19 and that she had an on-and-off sexual relationship with him over the course of a decade.
"I pray that we all get closer through this crisis," Chynna said at the time. "With prayer, anything is possible. But I would be lying to you if I didn't tell you that there are going to be some huge obstacles in front of us."
She also told PEOPLE: "It's such an uncomfortable subject for any family to talk about."
In September, the day before Mackenzie made her explosive claims, Chynna released her first album in years, One Reason, with Vaughn Penn.