I am still puzzling why so many people say that ancestry.com is phasing data. Here's one discussion about why family finder on FTDNA gets different matches. I don't really know what is true, other than ancestry.com says and people repeat that it phases. There was a report from a November 2012 FTDNA conference where they said they would start phasing as well...maybe this is different kind of phasing from what people have understood in past...everything keeps evolving!!
"Another difference is Ancestry is phasing the data, that is, sorting out which parent each letter of DNA comes from, to help weed out coincidental matches. It also enables them to find matches who share less DNA but who have to be dropped out of Family Finder because the data here is unphased."