Congratulations! That's a beautiful phal with two nice spikes. I repot my phals once a year (after they finish blooming) but if the media isn't breaking down you could go two years. Flush the media real well occasionally so that fertilizer salts don't build up in the mix. Aerial roots have a tendency to dry out in low humidity. I often mist the aerial roots to give them moisture but be careful not to get much water in the crown of the plant. You're done a nice job of growing that phal.