I would not be worried that he hasn't used a hide yet.
Many breeders use racks and do not have hides. Took Behira a few weeks to get into one, and now, she uses them, sometimes, or partially.
Is cool side 75-79? Or is ambient 75-79?
Ambient should be closer to 80-82F and cool side can be 78F or so, give or take.
If ambient is 75-79F and the hot spot is 90F (which I think should be 86-88F), then Phantom has no choice but to be on the hot spot to stay warm.
Make sure there is a gradient, raise the ambient, and lower the hot spot. Just my opinion.