By TNG Star Trek, the production crew made changes to the way things work in Trek and limited phasers to sublight-only.
Actually, they didn't. All we saw was that they didn't bother to show us any warp speed battles - from which it follows that we didn't see warp speed phaser battles, either, in contrast to all
the other Trek TV shows with their prominent warp speed phaser battles.
TNG did show us some warp chases where our heroes used torpedoes for defending themselves - but not in anger, not really. In "Encounter at Farpoint", they fired warp torps as a diversion, to blind the enemy without harming him. In "Best of Both Worlds", they did arm torpedo bays just prior to attempting a warp escape from the Paulson nebula, but they never fired those torps. And in "New Ground", warp torpedoes were used for thwarting the warp-speed soliton wave menace. There never was such a pitched battle at warp that a dramatic excuse for showing warp phasers would have existed.
So TNG failed to show warp phasers. All other TV shows showed them, though. And no show or movie, including TNG, ever had a character suggest that phasers wouldn't work at warp. To the contrary, in ENT "Fallen Hero", our heroes were agonizing over the problem that phasers, which obviously were supposed to work at warp, might not operate perfectly yet
, due to teething troubles. By the end of the episode, they did work just fine.