This is indeed normal, but I have to forewarn you... Don't get terribly upset if the bud does not open or it withers away and falls off...
Often times when you purchase an orchid in spike/bud and bring it home, it suffers bud blast
. What I mean by this is that the plant goes into shock from a transfer of growing environment. If this occurs, you did not do anything wrong - it's just that your home setting was radically different than where it was growing before you bought it.
HOWEVER, this does not necessarily mean that's what's going on. Check out your roots. Are they healthy? How often are you watering? Your roots should be a silvery-green if they're healthy and alive. If you have thick-brown, dark grey, black or spotted roots, your plant needs a new medium and a trim of dying roots to allow the healthy roots to absorb the proper amount of moisture and nutrients. Also, do you notice any salt build-up on the roots? Crystals that look like rock salt? If so, flush with lukewarm water for about fifteen minutes to wash it all away. When people water their plants with household tapwater, sometimes the water leaves deposits on the roots of your orchid that over time build up in the formation of crystals which can burn the roots.
All that being said... Are you fertilizing your little orchid buddy? It takes a lot out of the plant to bloom for you, so be sure it gets good nourishment. I can't really recommend one fertilizer over another, because everyone's growing environment is different and therefore each plant has different needs. As for me, I just use a general orchid fertilizer by Schultz, which you can find at most retail chain stores. i.e., Wal-Mart, Lowe's, Home Depot, etc.
One other thing... How many leaves are on the plant itself? The less leaves that are on your phal, the younger it is and the more it has to work to maintain and open new buds. The older phals get, the more blooms they produce and typically they hold the blooms longer (at least mine have). Phals produce on average one to two leaves per year of mature growth, so use this as a gauge to determine what the age of the plant is right now... This will let you know whether or not it's actually mature enough to continue blooming or if you need to go ahead and cut away the spike to permit the plant to put its resources back into root and leave growth for next blooming season.
I know this has indeed been a long reply to your original question, but I hope this provides an answer of some sort and if not I hope someone else will chime in where I left off