This is a one phase fight with just 1 major ability to watch out for: Overhead Smash. Basically Overhead Smash on 10man deals approximately 20k damage, reduces armour by 20%, and interrupts spell casting by 8 seconds. The armour reduction effect isn't too significant, however the spell interruption is quite detrimental.

At first I thought that if I could time it right, I can stop casting right before he uses Overhead Smash. However I could not find any timers in DBM indicating when Overhead Smashes are about to occur. Eventually I found that the actual frequency which this ability is used is rather erratic, it can occur as soon as 15 seconds, up to as late as 30 seconds, but most of the time it is used again before 20 seconds. Hence all my unsuccessful attempt on this boss was due my heals being interrupted. Even on my kill, I suffered heal interruptions for 2 to 3 times due to mistimed interrupts. Eventually I simply resorted to 15 seconds before I stop casting heals so he wouldn't be able to interrupt them (just to be safe).

Since I couldn't let the boss interrupt my heals, I resorted to using pure DPS spells (or instant cast heal spells) when he is about to interrupt. This means that a lot of my DPS spells were being interrupted. Hence the primary source of DPS ended being the DoTs.

If healing spells do get interrupted, I recommend to use Dispersion to minimize the incoming damage. Timing of his interrupts does get a lot better with more practice.