I keep my philodendron potted and it does great, I've never had any problems with it. They are decently cold hardy so you can plant them in the ground if you are willing to give them good protection, but I dont think it's worth the worry, they like being in pots anyways!
-Alex

I am also in zone 7b and quit growing them in the ground. They suffer too much even though they often survive winter. I still plant them in the ground and then just dig them up in the fall and keep them in a pot for the winter. To me, this is easier than lugging a large pot in and out. I usually wait until after first frost to cut them back (just the old leaves and long surface roots) sometimes its after the first hard freeze. They are very tough plants.

Any that have been left out all winter never get very big and I was going for the super large sized leaves.

I have several tropicals and subtropicals but bring them in the garage into a plastic walk-in greenhouse with grow lights on a timer and a small portable heater when the temperature goes into freezing and below. They do great in there, and I just water them a few times during the winter months. Then in mid-April, I start to harden them off for the summer in the garden.

All the replies are warmer zones than 6. If tropicalzone in zone 7 brings his/hers inside I guess zone 6 outside in the ground is not a good idea. I have seen them in our Lowes, and thought the same as vent1962. I have an outdoor greenhouse, but it will hardly get warm enough in there for tropicals. All I have are 2 doghouse heaters. I haven't tried them out yet. I think my basement will be their winter home. It's a constant 60+ F in winter with a south facing door. Half the door is clear glass.. I just bought a Bird of paradise today at Lowes. I saw them in Florida last spring and loved them.