Is it permissible for a girl to communicate by phone with non-mahram male colleagues after work hours to check on them, and is this considered an opening to temptation?

A woman's speech with a non-mahram man without need is a door to temptation and a means to corruption. It is permissible out of necessity if temptation is safeguarded against; otherwise, it is not permissible. The fundamental principle regarding a woman's work is that it should be free from intermingling with non-mahram men.