Timer question: Phase Correct PWM at specific frequency
pinMode(3,OUTPUT);

Pin 3 on the Nano is OC2B. It's PWM is controlled by Timer 2. You
want to use pin 5 (OC0B), since you are using Timer 0. Or
switch to Timer 2.

Phase correct PWM with top as OCR0A

Note that this is the description of mode 5. If you want this mode, you
have to set both the bit WGM00 in TCCR0A (which you did)
and the bit WGM02 in TCCR0B (which you didn't). Here you have set
mode 1: phase correct PWM with top = 0xff.