The Rising From the Ashes trophy relates to a late game quest, where you have to, as the description says, “rescue the phoenix.”

In order to unlock this trophy you need to complete the “Phoenix Rising” side quest, which is available if you talk to Deek in the Room of Requirement after completing “Niamh Fitzgerald’s Trial.”

In the quest you’ll head to the aptly named Phoenix Mountain Cave (not very elusive, eh?) in northern Poidsear Coast. Complete this quest, get yourself a phoenix, unlock a trophy.