Does yawning accompanied by a sound invalidate the prayer, and does coughing accompanied by a sound and an attempt to expel phlegm invalidate the prayer, especially if the act is repeated multiple times?

Yawning audibly with a sound, if it is involuntary, does not invalidate the prayer. As for coughing audibly with an attempt to expel phlegm and its repetition, if the person is overcome by it due to illness, their prayer is valid, even though some scholars consider prayer invalidated by frequent coughing, even if involuntary. However, prayer is invalidated by intentionally yawning or coughing audibly such that two or more letters become apparent.