So I've been roped into fixing an old Boss PH-1 phaser. Usually the ones I get given are loose wires, shitty switches, stuff like that, but this is beyond me.

When it's plugged there is no signal through either the effect or the bypass buffer, although when the effect is on a phasing sound can be heard (just a swooshing sound that is affected by the knobs), which would lead me to believe that there is somehow a problem between the input jack and the phasing/buffering section of the circuit, however I've tested wires and components in that particular line and everything appears to be in order.

Have you guys got any other ideas?
Are you absolutely positive that the switch is good and is properly wired? Are the correct voltages getting to the correct points in the circuit?

Here is a schematic.
I get continuity through the two contacts on the switch when it's pressed down. (I'm not so good on the Boss style switches, is that right?)

Where would you recommend I test for voltage on the circuit? A source in a deep, dark corner of the Internet told me the two ICs are for audio amplification, and the phasing itself is done by the transistors, but I don't know how reliable that is...
That's basically correct. Test between pin 6 of each IC and ground. Also test continuity between pin 11 and grounded battery terminal to make sure these pins are actually grounded.

Also check for voltage at the cathode of D1, + end of C20, and the supply ends of R24, R38, R39, R42, and R43.

Finally, make sure the input jack and adapter jack are properly switching the -lead and +lead of the battery, respectively.