There is a small trick that if you trigger Dreadwyrm Trance and let it run out without summoning Bahamut, you can simply wait (while having Bahamut on hold) for the cooldown to wear off. Once it did, you can summon Bahamut and immediately have Phoenix ready to go as well, once the former finished its buisness. Not many People do that for some reason but it does look cool if you do so.