Many types of philosophy can be relevant to your life as a business manager. On a practical level, logic will help you make good decisions. Logic can also help you spot errors in reasoning and make you less likely to be taking in by marketing ploys or flattery.
On a ore important level. ethics can help you think through how to behave as a manager. Although much of your job is focused on the "bottom line", you also are a corporate citizen and world citizen. Thus you need to balance paying a bribe to an evil dictator, hiring child labour, or polluting the environment which might bring short term profits will also cause harm to you and your world. Ethical systems can help you make informed judgements about the moral value of your actions.
As well, being a business manager is only one of your roles in life. If, for example, you are offered a promotion that might take you away from home and family, or you have an opportunity to follow a dream or do good for humanity at a lower salary, philosophy provides a good beginning to helping you think about what your ultimate ends in life are.
Ethics: A Very Short Introduction. Simon Blackburn
Enchiridion (or Handbook). Epictetus.
Apology of Socrates. Plato.