The phrase "in someone's opinion" can be replaced with several synonyms that convey the same meaning. One such synonym is "according to someone," which denotes that the information or belief is based on the perspective of another individual. Another synonym could be "as per someone," which implies that the statement is in agreement with another person's view. Additionally, one can use "in somebody's view," which communicates the notion that the stated point of view may differ from one individual to another. In conclusion, these synonyms enhance clarity and eloquence in communication, allowing one to express perspectives explicitly.