Phrase It Right lists synonym phrases which are similar in meaning, but may not be identical. You can check the exact meaning using a suitable website and use the phrase that best fits the context.
Subtle changes in meaning, lending variety and vividness to the writing, can be achieved by avoiding repetition of the same phrase in the document.
Register relates to the amount of formality or informality that a language has.
Formal: make a mistake
Informal: mess up
As phrasal verbs are often informal, a synonym can be used, where appropriate.