The phrase "occur simultaneously" implies that two or more events are happening at the same time or synchronously. However, there are several other synonyms that can be used to convey the same meaning. Some of these synonyms include "concur", "coincide", "parallel", "co-occur", "simultaneous", "synchronous", "together", and "concomitantly". These words can be interchanged depending on the context in which they are used. For instance, "coincide" suggests chance or accident, while "parallel" implies a more deliberate and planned alignment. In conclusion, a writer or speaker may choose to use any of these synonyms to add variety to their language or to convey a more nuanced meaning.