I finally got around to reading my April edition of Orchids Magazine from the AOS today and it's interesting that one story was on this particular subject
The article says that although most Phals will rebloom on the same stem, the blooms will most likely not be of the same quality as the first blooms were. The spike, whether in bloom or not, continues to sap strength from the plant. They suggest cutting back the stem to allow the plant to concentrate on producing another stem with blooms of the same high quality rather than allowing it to grow and probably getting an inferior bloom.
I have a few that have rebloomed and it's true...the second blooms are lacking. I will be cutting my spikes back when they're done...it'll be hard but I'll be brave and get it done
tfields 
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