Straight and level..Power controls speed. Pitch controls Altitude(Vert speed)
Yet as the speed increases the pitch is lowered, so they interact!
Climb....Power controls Vert Speed. Pitch controls forward Speed.
You could also argue that Power controls forward speed. if you reduce thrust while maintaining pitch the speed reduces. Then if you lower the pitch it controls the vertical speed as well as forward speed. Pitch and power interact!
Descent...Power(or lack there of) controls Vert speed...Pitch controls forward speed.
See above
Approach Power controls forward speed pitch controls Vert speed(glide path)..however...if excess deviation occurs on glide..use power reduction(if above sope) or power increase(if below slope) appraching half FSD.When at or beyond half scale dev..consider Go Around.
Increasing power adds energy to the airplane, the pitch determines if this is converted into speed/vertical speed/both. If power response is fast enough nothing might happen as the energy added counterbalances the upset that required the extra energy.
Likewise with decreasing power.