It isn't black and white like that. The team always has a voice and can express it at any time. Communication is always key and that is the whole point of developers pointing stories. They could just call a story 8 points and the PM would never get it into the backlog. =)
The PM is the conduit between the business needs and the developers. The PM and the lead team dev decides the backlog. Devs just pick the next story from the queue, but of course they have input on things as well and can convey this in any of the meetings or directly with the core dev or PM.
