Claremont had little interest in doing that, and six years ago he more or less made it impossible (at Jim Shooter's insistence), by killing Jean Grey after she, as Phoenix, had caused a genocide. If you want those original five back, you have to resurrect Jean, but her death was her absolution. If she is simply brought back to life, she will be unredeemed.
This, though, is not an insurmountable problem. It's Marvel Girl they wanted back, anyway, not Phoenix, so if we rewind the clock to when Marvel Girl became Phoenix, there's a natural point to insert a swap. In this case it is supposed that the Phoenix force created a copy of Jean and was wandering around in her place - and that it's responsible for the destruction of that Shi'ar sun, not the real Jean Grey, who is safely cocooned in Jamaica Bay, still.
The story goes out of its way to emphasise that the Phoenix duplicate was identical to Jean in every respect, and that it was Jean's humanity that was responsible for the Phoenix's sacrifice, in a way that is supposed to absolve her. But if the duplicate really was that good, then wouldn't she have reacted in that way, too? Sure, it wasn't actually her who did it, but there's no need to be quite so smug. They could have gone another route here, and had the Phoenix be an imperfect copy all along: certainly Scott never seemed to reconnect with her - and had trouble mourning her, even.
Ignoring the philosophical problems with the story (and let's face it, it's not the most morally objectionable thing to happen as setup for X-Factor), mechanically it's handled competently enough. You can see in Fantastic Four #286 a strong engagement with the details of the original story, in a continuity-obsessed way which anticipates Byrne's approach to The Hidden Years. Yes, it makes sense that she thinks she's still fighting Lang and his X-Sentinels, but she has been unconscious for a good long period: she didn't need to remember it.
So, what next? The Fantastic Four and Avengers don't think she should go back to the X-Men: they're working with Magneto. But Reed has an idea for someone he might call...