From this non-canon source and what I understand from watching various episodes, there were three buttons on the Type-II Phaser from TNG onwards:
A number of questions remain unanswered, however:
- Main trigger button
- Forward left for intensity
- Forward right for beam width
A number of questions remain unanswered, however:
- How many beam widths are there?
- What sequence does the beam width increase with each button press? (1-2-3-1-2-3 or 1-2-3-2-1?)
- How is the change in beam width denoted? A separate display? Beeps of increasing intensity?
- How would one remodulate the frequency for dealing with Borg? Is there a hidden adjustment interface in the phaser itself, or is an external tool used?
- How would one set the phaser on overload?