A few years back I was at the Tamiami Orchid Show and heard a local vendor (I had never met before and can't remember) discussing with a local hobbyist about putting Phals. on trees in the Miami area. I'll report what I heard:
- Put them in full shade all day. They scorch quickly with just a little summer sun.
- Tie them on the trees sideways, so the leaves hang down and the crown will drain water quickly.
- Miami Winters are really too cold for outdoor Phals., so you should expect losses every year. The big white ones seem to survive the longest. Sometimes you will find one that lives for many years.
- He suggested buying discount grocery store Phals. for mounting on trees, since there will be so many cold weather losses.
- Water every few days in Summer if it hasn't rained. Water during warm times in Winter.
- If they survive they will flower without fertilizer, but of course fertilizing will lead to better flowering.
From the above I wouldn't put them on a palm trunk unless it's in full shade from other plants. You might be able to put them up in the crown if it's the kind of palm that has some dense shade up above. Coconut palms and other feather palms don't. Some of the Sabals might.
I gave a friend in Pompano Beach a Vanda seedling and mounted it on the North side of a coconut palm in her front garden. It soon attached firmly and began to grow. She said it bloomed when it got bigger.