If my BMI is 27.3, is it okay for me to take phentermine 37.5 under a dr's supervision for a month?

Can't answer. First of all, no one on an app can truly answer that. Your doc needs to know your medical conditions, medications, pattern of weight gain, etc. Secondly, i'm not sure a doctor would prescribe it for a bmi of 27 anyway. You should be able to get out if the "overweight" zone with simple diet and exercise. You can do it! don't take a pill. I have faith in you! good luck.