The legendary singer opened up about his 19-year-old daughter Sofia's relationship with 34-year-old Scott Disick, telling The Daily Telegraph she's at an age where she thinks she knows everything ... but he's not so sure.

Lionel says of the couple, "Is it going to be for life? I don’t know. But for right now it’s just a phase and I’m going to stand real still in the corner, get me a good drink and not make too much noise.”

Richie likens the situation to when he was Sofia's age, rocking an Afro and telling his father he was in love. He says his dad ignored it and let him figure it out, and adds ... "My daughter is getting me back for my Afro days!"

When we last checked in on Sofia and Scott, she was dancing for him in a skimpy Santa suit ... to Lionel's music.