Words that are synonymous to the phrase "stand upright" include "stand tall," which connotes a sense of pride and confidence. "Stand erect" is another possible replacement that conveys a sense of formality and proper posture. "Stand straight" is a simple and straightforward alternative that emphasizes the importance of maintaining a vertical position. "Stand at attention" can evoke a sense of military discipline, while "stand poised" suggests balance and composure. Additionally, "stand up" and "rise" are more general alternatives that can also apply to situations where one is getting off the ground or otherwise elevating themselves.