Phasers are super versatile but they need to be programmed. That's not something you want to be doing on the battlefield - which is why the default function is "point and click to shoot".

And most of the time we see phasers used - aside from the occasional stone heating or vaporising - it's in a battle situation where reaction time matters. Tuvok had a moment to set things up, but in most other situations, that moment might be deciding if you live or die.