This isn't really what happens, but it's close enough: Protagonist is in a car. Dialogue is occurring between her and her husband, giving a smidge of background. Cell phone rings, call is from husband's brother, who is on the verge of dying in the midst of a natural disaster on his end. I want to transition the story from the the protagonist's car, to the other end of the phone. But ... I just figured out how to do it.
Just cut to it. Either with a new chapter, a break in the chapter or even just starting a new paragraph. It's not like you can do a star wipe.
I think for a more seamless transition you can have the dialogue in the car include its own kind of tension. To go from some casual chitchat to this panic situation might be too abrupt. Perhaps the couple is fighting about something, the tension in the car growing and growing with every rebuttal and broad claim. Finally, at the highest point of their argument, this call comes and takes that same tension to the husband's brother's situation.