Setting up VoiceAttack for use with PF3 ist pretty much straight forward.
Create a profile called "PF3" or whatever you like, create a new command with the phrase you want to use and assign the KeyPress for the respective PF3-hotkey. Repeat for all the phrases you want to use.
Additionally I add a short sound (like a click or a radar noise) to be played, so I know immediately if VoiceAttack picked up my command.
Optionally you can set a push to talk button by assigning a "Recognition Global hotkey" under the "Hotkeys"-options. Choose the same key you use as a PTT in PF3.
Example: Request initial clearance
New Command:
When I say: "ready to copy"
Other/sounds/play a sound: <your .wav-file>
KeyPress/Press and release key/hold down for 0.1 seconds: <your PF3 communication key 0-key>
Now you can hold the PTT and say for example: "Kennedy Tower Delta 1495 with information oscar, ready to copy, IFR Atlanta". Make just a short pause before and after "ready to copy" so that VoiceAttack can pick up the command.
You will hear the sound you assigned and VoiceAttack will send the 0-hotkey to PF3.