Guild Glory of the Cataclysm Raider

10 man Classic (AQ10): 8 Guildies
40 man Classic: 10 Guildies

10 and 25 man TBC raids: 8 Guildies

10 man Lich King: 8 Guildies
25 man Lich King: 8, 10 or even more(?) not sure, the achievement is the same for doing it in 10 or 25man.

10 man Cata: 8 Guildies
25 man Cata: 20 Guildies

By the way if you are wondering how to tell whether your party is a guild party there is a icon on your minimap that says it at your mouseover

It's not like everyone in the guild is automatically mailed this when their guild kills the appropriate bosses. There are still individual requirements that you must meet before you can obtain this mount. #1. When guild completes this achievement, the Dark Phoenix mount becomes available to purchase on the guild vendor. #2. YOU MUST BE EXALTED WITH YOUR GUILD TO PURCHASE THIS MOUNT. #3. The mount costs 3000g to purchase. This means that only loyal members can actually purchase the mount and that it will not be possible to sell it to players by inviting them to your guild and allowing the