I was having this problem on my 3 year old Phaser 850 as well. Started jamming on exit, with no visible obstructions. Then started jamming on the high capacity tray.
I read the posts about using small cable ties to repair the maintenance tray lift arms. This helped a little, but within a few days, my printer started making horrible banging noises, shuddering and other not healthy noises for a printer.
Correctly assuming that the cable ties were obstructing free movement of the lift arms, I removed them (the cable ties).
I then grabbed a small tube of JBWeld, and carefully added just enough to fill in the worn areas on the maintenance tray lift arms.
After curing, (24 hours) I used an emery board to carefully file down any excess JBWeld on the sides, top and bottom of the lift tabs. Carefully reforming the original bottom straight edge of the lift tabs.
Still had the same problem. Banging, bad noises ect.
It would print fine in full duplex, or if I was printing a presentation that had a significant pause between printing pages. But it was still LOUD.
So, I pulled out the maintenance drawer for the 32nd time and reached inside the cavity to run my fingers across the two lift arms. Sure enough, a nasty little plastic burr, was catching the lift arms and causing enough delay to give the printer fits.
After carefully knocking the burrs down, I used a q-tip to rub a small amout of silicon lubricant on both the lift arms and maintenance tray lift tabs.
This seems to have done the trick.
Bottom line? DO NOT USE CABLE TIES TO REPAIR A PHASER 850 WITH WORN LIFT TABS! They will kill your printer if you are not careful.
The cable ties add additional material on the top of the lift tabs, which bangs up against the stop, prematurely, and before you know it. big trouble.
If you do attempt to repair these lift tabs, I would recommend the JB Weld process above, or getting some shrink wrap tubing of the appropriate size, and only cover the actual worn area, shrink it down, and be sure to lightly lube mating surfaces with a little silicon.(Shrink tubing is about 1/5 the thickness of a cable tie.)
The Silicon lubricant is a very important final step.
Hope this helps save someone a service call.
Cheers,
Scott