Brandy says she got to tell Whitney Houston how much the singer meant to her right before she died ... and she felt the star was changing for the better.

The Grammy winner stopped by "Good Morning America" to discuss her new memoir "Phases" ... and she pulled back the curtain on her final conversation with the music legend -- during which she told Houston just how much the star impacted her.

She says she told Houston she inspired her and loved her ... and despite not knowing Houston would soon pass away, she calls it an "emotional" conversation nonetheless.

Tragically, Brandy says she really felt Houston was going to turn her life around, and the two would once again establish a close relationship ... but it obviously didn't turn out this way.

In "Phases," Brandy says this chat went down in February 2012 while she and her collaborator Monica were rehearsing for Clive Davis' Pre-Grammys bash. Houston gave Brandy a note, she says ... and the two talked for hours on the phone that night.

Just days later, Houston was found dead at the Beverly Hilton Hotel in Los Angeles. Authorities ruled drowning as her cause of death, and a toxicology report showed numerous drugs in her system at the time of death.

Brandy's peeling back the layers on lots more of her life in the new book as well ... including revealing she dated Boyz II Men star Wanya Morris when she was just 16 years old.