Though Phoebe was working as Massage Professional, why did she hate massage parlors? And convincing her friends not to go there?
I'm guessing you are talking about the episode The One With The Fertility Test (S9Ep21):
Rachel receives a gift certificate to get a free massage at a chain massage center, which Phoebe doesn't want her to take advantage of as she feels it takes away business from independent massage therapists like herself.
What Phoebe doesn't tell Rachel is that she's one of the employees at the very same massage center. However, she has a hard time concealing her identity to Rachel, her client, during her massage.
While Phoebe hates these massage chains she works for one
... because it's good money ... and they give me benefits, like medical and dental...
but she admits about feeling ashamed
... because I sold out for the cash
As stated before, this is the episode that comes to my mind.
To answer your question, I think a simple example in the real world would be a local Mom and Pop store, v.s. a big chain store such as a Wal☆Mart... The obvious analogy being that businesses like Wal☆Mart drive smaller independent companies out of business.
ON ANOTHER NOTE... Phoebe did work for a smaller independent parlor before being employed by the chain. She is only working there to make her ends meet, and survive, since we know she is a survivor from her days on the street.
She is also hiding the fact that she works at the chain parlor because it is known within the group of friends that that sort of business is against her beliefs and morals. If she were to come clean about working there initially, she thinks that her friends would see it as her not sticking to her morals, which again, is what Phoebe is all about.
Of course we all know that Joey, Rachel, Monica, Ross, and Chandler are great friends, and would have never accused Phoebe of abandoning her morals, but Phoebe just wants to save face, as we also find out is very important to her when she meets Mike later on.