Live view uses the main sensor image output. It looks at the contrast and tries to get it so whatever you're pointing at is sharp. With DSLRs though, this is a generally slow process as they were never originally designed to do this. Assuming you don't have a complex shape or pattern, then it will get it right more often than not, and there is not much room for error.
Phase AF uses a separate sensor located in the bottom of the mirror chamber. This gives the body more information about distance and amount of defocus to go on, but you're relying on a fair few assumptions here to give the same focus at that point as the main sensor.
On the front focus, from what I recall of previous threads the "error" wasn't that great anyway, with the actual focus lying on the edge of the depth of field of the desired focus. I don't know about other countries but Sigma UK will adjust a lens to a body if you supply them with both. The other option is to replace the body with one that supports micro-adjust, so you can set the offset yourself. Practically speaking that means either a 50D (not 60D) or 7D.
_________________Canon DSLRs: 7D2, 7D1, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 10-18, 15-85
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 50/1.4A, 150 macro, 120-300 f/2.8 OS
Compacts: Sony HX9V, Fuji X100.