Had a little time to sit with my AxeFX this morning and did some experimenting with the phaser.
Disclaimer: I'm a Jerry guy ... I don't have a great Bobby guitar or Bobby chops.
I first tried to set up a basic rendition of Weir's tone as I hear it today, clean, bright, with some bottom to it. I did that by creating a very simple patch in the AxeFX, using a Mesa Boogie clean amp, a custom IR I made of my JBL K-110 speakers, and a pedal style compressor. This is all direct ... PRS Custom 22, both pickups, split coil -> AxeFX -> Apogee Duet on my Mac Pro into Logic 8 for recording.
I would not say this is a great Bobby patch, just a very basic one. It took all of three minutes to create. No EQ, etc. I could've used my Strat or Tele, but the PRS was handy.
I played a little of a Ratdog tune, She Says.http://www.playingdead.net/weirclean.mp3
Then I used the same patch with a little slap delay on it, since I seem to hear a slap on his guitar lately.http://www.playingdead.net/weirdelay.mp3
Then, I shut off the delay and created a phaser block in the AxeFX, 8 stages (I think that's what the Ibanez multieffect units had), and assigned the sweep to my expression pedal. Moving the pedal moves the sound through the various stages. There is a lot that you can tweak within the phaser block -- number of stages and the regeneration and feedback have huge effects -- but I didn't get into much of that. I just wanted to see what it would sound like.
A little Not Fade Away, just moving the pedal a little at a time.http://www.playingdead.net/nfaphase.mp3
Then, a little half-assed Wharf Rat, doing the same.http://www.playingdead.net/wharfphase.mp3
It's a very broad palette of sound you can get by moving the expression pedal. I would think that with a real Cowboy guitar and the pickups set the right way, you could easily figure out where the pedal should be and lock down the phaser for that 78-81 tone. On the AxeFX you can also modify the ramp that the expression pedal will travel, so instead of 0 - 100 percent on the sweeps, you could put it from, say, 40 percent to 60 percent. I suspect that's more what Cutler's pedal did, because there are certain songs from that era, like He's Gone, where you can hear Weir varying the sweep while he's playing, and it's not nearly as broad or through as many stages as the AxeFX will go with the full sweep.
Note that the rest of the patch is the same, so you can hear what a huge difference the fixed phaser makes to the overall tone.
I also assigned a wah to the pedal at the same time, which works, but it would take a lot of time to fine tune the wah range and the phaser sweep to be workable together, so I didn't mess with it.
But I've always wondered about this, and I think it's a significant part of how Bobby got that particular sound from that era.