Dear N:

You wrote:

1-That was his first movie with Sidney Poitier.

2-That was his first movie, with Sidney Poitier.

In 1 it is clear that ‘his first movie with Sidney Poitier’ forms a single noun phrase. (It was not his first movie. It was his first movie with Sidney Poitier.) Does the comma in 2 make ‘with Sidney Poitier’ non-restrictive? Does 2 correspond to

3-That was his first movie, in which Sidney Poitier had a role.

Good question. The short answer is yes, the comma in #2 implies the phrase is nonrestrictive.

However, sentence #3 needs a word like “also” or “too.” Such a word might help #2 as well. There are ways to make the sentence #2 clearer, e.g. “That was his first movie, and Sidney Poitier was in it, too.” While the restrictive/nonrestrictive rule is clearer with clauses, it does apply to phrases as well.