[header] How to get someone to stop talking loudly on their phone [title] Isolate the loud talker. [step] This will allow you to address the behavior without embarrassing the caller or making a scene in public. See if you can take the caller aside to a secluded corner, office, or wall. 
Address them formally, and be as polite as possible. [substeps] Ask the caller something to the effect of, " sir/ma'am, can you talk a bit lower? Your voice is carrying.