2.5~3k MP should be fine entering golem phase, golem phase requires very occasional healing (Demolish = medica 2, the mountain buster-ish attack from green golem), thus you should be able to regenerate a respectable amount of MP (you can shroud 2 times here, 1 at the beginning of golem phase, 2nd during megaflare countdown).

I am able to enter Heavensfall phase with 4k MP consistently thanks to the huge amount of healing downtime in golem phase (Yes I can help to dps, but the entire golem phase is completely time based, you can't "push phase" if you dps faster, so I just assist in killing the 1st golem to prevent color change, and then /mdance while the dpsers do the work).

In conclusion, your MP entering phase 2 seems to be fine, just utilize phase 2 to regenerate as much MP as you can, good luck!!