My suggestion would be to repot instead of trimming the roots. I think it's so much easier to repot.
I just feel that Phals are too much of a pain to grow to even risk causing it that kind of damage. Yes, they do go through a period where they stop growing in order to recover. Some may not, it depends on the individual, keep that in mind too.
Keep in mind that nurseries also deal with plants in
bulk. If one or even 2% of the stock dies because it couldn't recover from the damage from trimming the roots, they're not crying so much. If your one plant croaks, you could be hurtin'.
Then there's the whole being mindful to sterilize the cutters between cuts. That's even more bothersome.
I'll also put it another way...
Do you really want to take an unnecessary risk?
Think about what the possibilities are for the action taken...
There are actually quite a few things that can happen from cutting roots, beyond just seeing the roots cut.
This is my
.
But if you want to trim thems roots, it's up to you.