The phrase "think up" means to come up with or devise new ideas or solutions to a problem. If you're looking for synonyms for this term, there are several options you can use to express the same sentiment. You can say "conceptualize," "invent," "imagine," "create," or "formulate." You can also use phrases like "dream up," "hatch," "conjure," or "cook up." These synonyms all convey the meaning of generating new ideas or solutions, but each one may have slightly different connotations or implications. Choosing the right word for the situation can help you communicate your meaning more effectively.