Hello, Her incinerate damage has been bugged for a long time.. It says it deals like 115% of her attack over 6 seconds (5* 3/45)
Phoenix had 1376 base attack rating. With 5 furies her attack would be (1376 + (5*156)) = 2156 * 1.15 = 2479 damage over 6 seconds which should tick for 206 damage per second. It only ever ticked in the 20's or with 5+ furies only 30-40's against Winter Soldier.
https://www.youtube.com/watch?v=Ys04o-Zgjrg - Seatin's rank up and gameplay video, you can see at 16:00 or 17:00 minute. You can have 10-11 furies and 10+ incinerate stack's but this damage it's very low.