|You sent a loud and clear message to your manager about a co-worker whose speakerphone is too loud and clear, but your manager essentially ignored it. It's time for another message.|
Since you have co-workers who are also being disturbed by this individual's discourteous decibels, you should team up with them and then approach your manager. Let your manager know that the volume of your co-worker's voluminous calls is interfering with your ability to carry out your responsibilities, and the result is a decrease in concentration, productivity, and overall performance.
Tell your manager that you need his help because all of you have tried to deal with this matter without any success. However, instead of merely complaining, try some suggestions. These are up to you, but they can include moving the loud speaker and his loud speakerphone to another area, implementing a policy that prohibits the use of speakerphones during work hours, or firmly advising this employee that his behavior is interfering with the work of others and it needs to cease immediately.
If your manager still opts to do nothing about this, you should consider contacting his manager, but not by speakerphone.