The phrase "a great extent" is commonly used in writing and conversation to indicate a large amount or degree of something. However, there are many synonyms for this phrase that can add variety and nuance to your language. Some alternative phrases include "to a considerable degree," "to a significant extent," or "to a large extent." Other possible synonyms include "to a substantial degree," "to a considerable extent," or "to a vast extent." Additionally, you might consider saying "to a good extent," "to a fair extent," or simply "largely" or "mostly." Experimenting with these different synonyms can help you to communicate your ideas more effectively and expressively.