uh oh, now you've done it. this is how orchids reproduce--they sit
there looking pretty so you bring them home as presents, and the next
thing you know, you need to buy more and more of them. remember:
they're like potato chips--you can't have just one.

anyway, that said--yes, pull off the wilted flowers, no problem. phal
flowers can last anywhere from weeks to months, depending on the
plant. also, if the plant was in bloom when you bought it, there's no
way of knowing how old those flowers were. phals bloom annually,
usually, and the plants can live for decades with the proper care.
here is a general culture sheet from the AOS:

http://www.aos.org/AM/Template.cfm?S...entDisplay.cfm

or

http://www.aos.org/Content/ContentFo...termedphal.pdf

where are you located? it sounds like you're giving it the right
amount of light, but care varies according to your climate.

congratulations (or condolences) on joining the hobby. ;-)

--j_a