What is the ruling on my action of speaking on the phone, which led to an argument between two colleagues and a physical fight, given that I feel guilty about it?

The question is unclear, but there is no harm in a manager blaming and reproaching an employee who has fallen short in their duties, provided that a good and gentle approach is used, and raising one's voice is avoided. This is based on the Almighty's saying: "And tell My servants to say that which is best. Indeed, Satan induces [dissension] among them. Indeed, Satan is ever a clear enemy to man" and His saying: "So by mercy from Allah, [O Muhammad], you were lenient with them. And if you had been rude [in speech] and harsh in heart, they would have disbanded from about you. So pardon them and ask forgiveness for them and consult them in the matter. And when you have decided, then rely upon Allah. Indeed, Allah loves those who rely [upon Him]." It is not permissible for one worker to strike another without justification. There is no blame upon you if you did not command or permit the striking, and the sin rests with the one who struck. If you have mistreated the workers with your speech, then you must seek their forgiveness and appease them.