Wow! That's a real root-bound orchid. If this were mine, I would select a pot a couple inches (max) bigger in diameter. I would soak the whole root mass in water to limber-up the roots (get them as flexible as you can.) Then I would tease the old bark out of that root mass. The idea is to get the whole root mass as free of bark as possible. Then I would study the whole plant to determine where the next growths will appear and attempt to get them as far from the new pot edges as possible, and still fit the plant in the pot. I would then start pouring the new bark mix into the pot while making sure the crown (the part of the plant that used to be at the surface of the mix) stays where the new mix will end up (the new "ground" surface). This almost takes 3 hands to do
. Then I would bang the pot down onto the surface of a table to pack down the bark. If you attempt to do this like you would a begonia or something like that you will break off many of the roots. So you want to do a steady tap-tap on the table to shake the bark pieces down. After the last level is in place water it in and you should be good-to-go.
As a side note, all my repotting is done with potting mix designed for a particular species and that has been soaked several hours in a mix of RO water with Dynagro KLN mix (1 tsp/gal), Dynagrow Pro-Tekt (1 tsp/gal) and MSU mix (1 Tblsp/gal). This gets 'em goin'