Phase is a really easy experiment - just swap the speaker cable connections. You'll hear the difference, no question! There is no way to be sure whether an amp is in phase or out of phase with the input signal, the specs are just not always correct even if there are some. That's the real reason I like banana plugs... :^)
I could tell you that most of our preamps reverse phase, and most of our power amps preserve phase, and I'm probably right unless you crossed up some transformer terminals or my memory slipped up. But it's way better to test it yourself. You may even discover that - in your room with your music and your setup, the "wrong" way sounds better. It happens.
You know, I spent a career in acoustical research. Did an awful lot of mathematics, and I always mixed up the phase on complex numbers, it's just way to easy to do that - physicists use i and EEs use j for the imaginary unit, and i=-j, and acoustics draws about equally from both disciplines. So I learned to ignore the problem until the very end, then try the result both ways and select the one that looked most plausible. Much more reliable and much much faster than making a theoretical analysis! If anybody pointed out an error I made, I just said "thanks" and made the change. Didn't happen very often.
