I think my Phal needs repotting - first orchid

[Wadelweiss]

Hi guys, I'm a relatively new new orchid owner, I own a odontoglossum which is looking a bit sad for itself and a happy Phal that I think needs repotting. It's finished its flowering and has grown two large new leaves. I've read that they like to be pot bound but I don't know how much is too much. It's currently in a 12cm pot, I'm thinking it could cope with a 15cm pot but don't want to upset it with it growing so well. Any advice would be really appreciated!