We usually have this thread about once per year.
My experience with weight lifting was pretty typical, I thought, of most men in their late teens and 20s. If you're not taking drugs, and you're busting your ass in the weight room for at least an hour a day, 5 days a week, a pound a month of muscle would be an excellent gain. That's 12 pounds a year.
Their is a very widely spread myth that a man can add "15 pounds of muscle in the off season." That's complete horsesh-t, unless you're on steroids. At that rate, you could put on 30 pounds of muscle a year and go from a 160 pound weakling to Arnold sized in 3 years. That's not how it works.
Phil did not - repeat, did not - put on 20 pounds of muscle between April and September. 10 pounds of muscle over that time period would have been a tremendous gain. If he put on 20 pounds, it was mostly fat.
Regarding training for vertical - pretty darn easy, really. Olympic squat athletes all have tremendous vertical.
When I started playing ball, I had about a 24" vertical. Pathetic. After about 4 years of heavy weight training and playing ball, my vertical was about 36". Acceptable. But my squat went from sets at 110 to sets at 300 over those 4 years.
I'm also not a believer that muscles make you slower or bulker or any of that, unless you're Mr. Olympia size. Most 18 year olds with a natural frame, like Phil, would benefit immensely from putting on 25 pounds of muscle, for quickness, vertical, and all of it.
The Florida before and after pics are proof of that - they didn't get slower by getting more muscular.
Phil is Phil.