It's rather nonsensical to claim that phasers would destroy TIE Fighters based on the fact that TIEs are unshielded.
They may be unshielded, but they are armored. Of course, this armor has little to no protection against the ungodly powerful turbolasers and starfighter lasers of the Star Wars universe but...
Phasers? Haven't we already proven that phasers are by far inferior to Star Wars weaponry? I'll rely on the more-scientifically-minded of the forum to state their proof again, if they wish.
That and the TIE's reputation as being maneuverable and hard-to-hit makes the phaser point rather moot.