I am not sure if you mean natural pearl or genuine pearl in your question. A natural pearl is very difficult to detect, and can only be determined absolutely with an x-ray test.
If you would like to know whether or not a pearl is genuine, however, this is much easier. The easiest method is known as the 'tooth test'. This is a simple test preformed by rubbing the pearl against the biting edge of your front tooth. A genuine pearl will feel slightly gritty, while a fake pearl, or a bead designed to look like a pearl, will feel smooth.
If the pearl is from a saltwater variety, such as Tahitian, South Sea, or Akoya, you may also be able to peer down the drill hole to detect a nucleus. A fake pearl will not have a visible nucleus.
Regarding your question about pearls from the Philippines and Borneo; the Philippines are now producing large quantities of Golden South Sea pearls. Tahitian production has been attempted, but success has yet been fleeting. A company under the brand name 'Jewelmer' is dominating the Philippine production at this time.
I have not heard of a pearl industry in Borneo. I have heard of a company called 'Borneo Pearl', but I am under the assumption that this is a brand name, not a pearling center. I could be mistaken, but if pearling is an industry in Borneo I am quite certain it is in infancy.