Genetics are tge main thing. A phoenix has a set point that it will grow to each molt,,then hardens off. A good high protein diet is a good idea to help the males and keep hens from picking the blood feathers. But lines are the main thing. A good breeder line for example will massivly out grow a hatchery line bird.
Housing is what keeps the tails in good shape. Thick bedding and little to no pen mates is best for a perfect show male. Pens mates pooping and stepping on tails ia a sure way to get them ratty and broken. Fully roofed and dry pens are a must. Wet muddy pens are a no no. High perches help too.
But even with all this, if you are going to breed them, they be messed up in a couple.months. mostbthe nice pics you see are either isolated males, or ones taken right after the regrowth period is done... We all breed them of course, and it doesnt take long for a pen full of hens to ruin a nice tail