If someone were taking 37.5 mg of phentermine and consuming less than 700 calories per day, would that individual loose weight?

Probably. Since the normal daily energy loss runs from 1500=3500 cals, consumption of only 700 would eventually lead to weight loss. A pound is roughly 3000 cals, so whatever your daily deficit in intake to expended would eventually add up to weight loss, The amount would depend on your personal daily energy use.

If your calorie count is correct, you would lose weight with activities of daily living. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV and Covid vaccines. Wish you good health!