Does fasting become invalidated if stomach acid comes out with phlegm when one tries to expel phlegm forcefully?

The fast of one who is overcome by vomit and does not intentionally induce vomiting is valid, and he is not required to make up the day, due to the Prophet's (peace and blessings be upon him) saying: "Whoever is overcome by vomit does not have to make up the day, but whoever intentionally induces vomiting must make it up." As for one who intentionally vomits, he must make up the day.