I've been to the phoenix symphony a handful of times now and I always leave wanting to go back. There are no bad seats in the hall.The staff is completely professional and generally very friendly.
Here's a couple of tips if you want to go.
1) Bring cash for parking. I'm not even sure where you would go if you didn't have any cash to park. It'll cost roughly $12 to park in any of the nearby structures.
2) Keep an eye out for discounted tickets. the 2013-2014 season has been exceptional in regards to special offering for tickets. This is probably because of their lack of real musical direction while they search for a new Music Director/Conductor.
Try the symphony's website or living social for deals.
3) Take a coat. It can be cold in the hall. If you're a guy, you should especially bring one for your girlfriend who will inevitably get cold and take it.