My two biggest Phals are in clear plastic pots, too, and have become quite top-heavy. It doesn't help that they lean a bit to one side of the pot (as many Phals like to do). So I was trying to come up with a solution to this problem, too. I ended up putting the clear pots inside clay orchid pots like this:
https://www.homedepot.com/p/Southern...12OP/300208576
It's not a tight fit. There is still around a half inch between the two pots all the way around, but that works out well, because the plastic pots that these two are in have slots on the sides, too, and roots are coming out both the sides and the bottom holes. So I can fit them inside the clay pots without squishing the wandering roots, plus there's still good air flow.
It's nice to see how others handle this and get some other ideas.