While Michael was in danger, the Holy Phoenix also didn't get additional energy to repair her injury, and the holy Phoenix's own holy energy reserve was simply not enough to sustain her crumbling body.
Before Michael died, the holy Phoenix died first, and the body slowly dissipated into the air, leaving nothing but sparkles and some kind of ink stains, directly showing the true form of this holy Phoenix.
In the end, the holy phoenix was just a drawing that came to life, and when she died, she also had traces of ink that Michael used to create her.
The holy Phoenix died before she could persist, entirely because Michael, the creator of this holy Phoenix, was also in danger and he prioritized himself.
He took back all the energy he gave to the holy Phoenix to 'feed' her and used the energy to sustain himself.
He was trying to break free from the love virus and get back to Ainsley's body before the countdown to his death reached zero!