A good combo for the first phase is Dragon Slayers Greataxe + Lightning Clutch Ring + Hornet Ring, if you run far left to the left of the area with fog wall you can dodge the first demons jump and follow it up with a quick light attack, then about 3 weapon arts from the DSGa will stagger him and then a repost will finish him (Note: this won't work if you have phantoms as they will have more health and will not stagger as fast.), This can be done well before the second demon starts attacking you close up. Once the first one is dead the second one is easy. You could take him out the same way, but its easy enough to just take him out with normal hits.
For the second phase just learn the attacks and the DSGa Weapon Art can still hit very hard, but won't stagger as fast.