Boss Invincibility

For certain bosses such as the act 1 boss they have transitional phases before they can actually be defeated. I have on three separate occasions been attacked multiple times by these bosses rather than them going into phase 2. Essentially pitting me against a boss I cant damage. Is there anyway we can make it so once they hit a certain HP cap they automatically transform into phase 2? This would be like if Gael from Dark Souls 3 just stopped taking damage in phase 1 and continued attacking without progressing the fight. When you factor in the one shot potential all these bosses have in T15 and higher it feels very bad when you lose to boss invincibility.