Repotting large Phalaenopsis

[JLem]

I have a large Phalaenopsis currently potted in a glass cube - it was the centerpiece from a friend’s wedding a couple of years ago. It has done well, flowering twice. But it is toppling over and I think the glass cube is the wrong sort of container for it. So, I’d like to repot this into a plastic orchid pot. But I don’t know what size to use - everything I read says to use a pot one inch larger when repotting...but the original planting was not exactly correct to begin with. It’s current container is ~4” square. The leaves on the plant are 10-12 inches long and 2-4” wide. I’ve included some photos here, with a U.S. quarter for scale.

Any suggestions for what size pot to use? Other suggestions for repotting this? I should also probably mention that I have never attempted to repot an orchid before. Thanks.