That's not really true, speaking from experience. If you're overweight, you can lose that much in six months just from changing diet, eating much smaller portions, not eating at restaurants, taking occasional walks every week, and fasting (aka skipping breakfast). 2-3 lbs a week is very doable if you're kinda fat to start with and keep your intake reasonably healthy and varied, and a little below BMR. I think it's partially due to swelling and fluid retention, because obesity does increase inflammation and fluid retention from lymph etc.
But yes Phil looks like an Ozempic ghoul and absolutely lies about his fitness. He'd show every sign of having more muscle if he'd been working out for the past year and changed his diet. It's also soft confirmation that he probably has type 2 diabetes.