The antonyms for the phrase "climbing upon" would be "descending from" or "dismounting from". Climbing upon refers to the act of ascending or mounting on something, such as a ladder, tree, or platform. Conversely, descending from refers to the act of moving downward or stepping off something, while dismounting from means to step off a horse, bike or other similar vehicle. These antonyms provide the opposite meaning to the phrase "climbing upon". They convey the idea of moving from a higher position to a lower one, rather than ascending or mounting on something.