That's really, really tough. I would be down for a movie starring the original five, but I could see a trilogy with the All-New-All-Different group working out.
For the first movie, I would start with the Orginal 5 in a flashback for the first ten minutes or so. Flash forward a few years as Cyclops and Prof. X recruit Nightcrawler, Wolverine, Storm, and Colossus. The heroes undergo training and go on a mission to rescue the OG X-men from Stephen Lang in his research facility, resulting in a huge battle against Sentinels at the end. At the end Jean makes the sacrifice play and comes back as the Phoenix.
For the second, I would introduce Lilandra. Magneto has stolen Shi'ar technology and is using it to fuel a doomsday device that will destroy all humans on earth. Lilandra needs the technology to save her people, the Shi'ar. This time around Phoenix is fully used to her new powers. Rogue (and maybe Gambit) are added to the team. The X-men challenge Magneto and his brotherhood of evil mutants in the heart of his volcano base to save both the humans and the Shi'ar. In the end, Jason Wyngarde is revealed to be spying on Jean.
The third one would open in medias res, as they've been attacked multiple times by the Hellfire Club between movies and they rendevous at Angel's home in New Mexico. The heroes infiltrate the Hellfire Club and battle the Inner Circle after Jean is turned against the group. They beat the Inner Circle, but Jean becomes Dark Phoenix and flies of on a rampage, like in the comics. Also like the comics, the final battle pits the X-men against the Imperial Guard (who want Jean executed). Jean sacrifices herself in the end. After her funeral, Kitty Pryde arrives at the X-mansion, having just received her acceptance letter to Xavier's home for the gifted.