I'm in the same boat (and zone) as you Melinda. Would love to be able to grow big lush Philo's but no go here. I've been looking at (and attempting to locate here) Fatshedera lizzei (Variegatum). It's a cross between Fatsia japonica and Hedera. Big leaves, not invasive, needs some support to climb or will grow as ground cover -- and I like the look of it. Check it out and see what you think. I'd be interested to hear any other suggestions too.

Here is a link that might be useful: Fatshedera

Melinda, have you tried planting just a plain old $5.99 split-leaf philodendren like Home Depot sells as an indoor tropical? Here in 7b Birmingham, AL I've had several in the ground now for about 4 years & haven't lost one yet. They freeze to the ground when temps go below 25F & then I just cover mine with several inches of mulch. The trick to getting them to grow large again the following years is to feed them with some sort of organic fertilizer. I use fish emulsion, straight out of the bottle...not diluted. They love it.