My interpretation of the phone call is that it demonstrates the reverse causality that is now possible thanks to her new understanding. It doesn't mean the cause nor the effect are mutable, just that they are now accessible in a different order than is typical.
I think in the movie the decision to have the child is also immutable. So when in the final scene she commits to that path - it is because of the paradoxical freedom born of fatalism that she manages to be cheerful. There is literally no other way things could go - so why worry?
If she's selfish - she's deterministically, immutably selfish. Under the new model - the concept of a "change" to the future through action is incomprehensible. The future just "is".
There is nothing in the movie that explicitly supports this.
(Spoilers ahead.) My take is that as she learns the language, her mind is changed. Not only can she remember the future, she comes to understand that she cannot change it. Just like the other heptapod knew it was going to die, but came to Earth anyway because the future is immutable.
Giving her free will introduces a paradox: the future which she remembers will no longer exist if she veers off the path. Unless she can see all possible futures, which is a different story to Arrival altogether (see Dune). The whole visit could be pointless in any case (again, spoilers) if Earth decides not to help the heptapods in the far future. The entire plot hinges on an immutable future.
It's possible that she decided to have the child knowing what would happen to her, and that's why she can see that future, but that's still her making her own selfish decision. If she wouldn't have done that, then she wouldn't "remember" having a child. I think this is why they changed how the child dies from the book. In the book she dies in a perfectly preventable accident. In the movies is kind of pre-arranged. Making her die in an accident that the mother know is going to happen would have been very obviously evil when it's been proven she can sometimes act on knowledge of the future. The book makes the situation maximize the fatalism of the character: she knows her daughter is going to die in that climbing trip, yet she can't do anything to avoid it, she's just an observer, a passenger in her own life.