The phrase "burned up" is commonly used to describe something that has been completely destroyed by fire or heat. However, there are many synonyms for this phrase that can add more depth and variety to your writing. Some alternatives include incinerated, charred, scorched, roasted, seared, singed, blistered, and blackened. These words have slightly different connotations and can help you to better describe the intensity and extent of the damage caused by fire or heat. Consider using these synonyms in your next piece of writing to add more nuance and complexity to your language.