The short answer is that, in my experience, Delta is more likely to reward you on the back-end than with discounts at purchase.
By that, I mean, you will earn status through miles travelled, which in turn earns you things like free upgrades and additional flexibility when traveling.
Here's what I would do (keeping in mind that I'm a little bit obsessive when it comes to booking travel)...
Research the cost of booking four different ways:
- Normal return routing (i.e., MSP-PHX-MSP).
- Reverse return routing (i.e., MSP-PHX 1w, then PHX-MSP, then PHX-MSP 1w).
- Multi-segment routing in different combinations (i.e., booking multiple round-trips in a single booking).
- If your schedule (and patience) allows for it, also look at connecting flights like MSP-DTW-PHX or MSP-SLC-PHX (not sure if those routes actually exist, but when you bounce through a secondary hub, you sometimes can get a better price). This would add several more hours to each trip, which may be a huge hassle, and not worth it. I've also found that when I've booked this way, occasionally, the agent will offer to change my flight to a direct one for free when I check-in if there are any overbooking, weather, or other issues.
You may be able to get a better price by booking it one of these ways. MSP is a major hub for Delta, so you're probably paying a premium for that (their ticket structure gives preference to tickets booked THROUGH major hubs, not originating/arriving at, in my experience).
Do you currently have status with DL? If so, try calling the Premium Sales/Service line, and explain the situation to them. I've never had much luck, but they will try to help you. It also helps to call during an off-hour.
Another option would be to stop in to one of the MSP airport SkyClubs (PHX doesn't have one, if I remember correctly). They're usually much more helpful face-to-face. I remember back when you could actually walk in to a city Delta ticket office... those days are long gone.
Whatever else you do, make sure you also sign up for SkyBonus - http://skybonus.delta.com, if this is for business (and your company doesn't already have a travel arrangement in place with Delta). You'll need your corporation's Federal ID to sign up. It lets you "double-dip" in a way on earning miles... SkyMiles are yours, but SkyBonus miles become your company's. Both are valid for travel (under different schemes).
Aside from Delta, you've got a few options:
- Frontier Airlines (connecting in Denver). Smaller, so you may have better luck negotiating a better price.
- US Airways. I personally decided to never fly them a few years ago (very bad repeated experiences with them), but I do know people who don't mind flying them.
- Southwest. They fly between MSP and PHX. Their "coach" product seems to be less expensive, and their "business" product seems to be only slightly more than competitive coach. It still feels like being on a bus, though.