Uh so force fire works for Phoenix. Put it on hold fire - all my bombers are set this way anyhow - then click on the ground where you want it to bomb or fly over the units you want to bomb and wait until you're right above them before targeting them.
Same with TB.
I use 1-2 Phoenix to bomb light raiders that penetrate the front-lines or sometimes to bomb a line of LLTs, caretakers, or Pickets. They also survive AA better than Ravens, but since their damage is so much lower, Phoenixes are very limited in their usefulness. I generally build 1 to stop raiders and that's about it.