Depends on who you ask. I had two professors cover them. The first was in favor of the Sardinain/Western Med. islander theory. The second insisted we couldn't be certain, but suggested he believed it was a series of migrations and conflicts from a variety of sources. (Dorics pushing Myceneans abroad, possibly in conjunction with migrations from the Western Med., Greeks pushing Anatolian peoples out, etc.)

The main argument I can think of against a Phoenician origin for the "Sea Peoples" is that the Egyptians were fairly familiar with the Levant, so might be expected to use a less generic term when referring to them.