That would depend on what your definition of a 'modern fighter' is! Airframe vs airframe it would certainly struggle against most fighter aircraft brought into service in the last 10 years. I suspect it would also struggle 1 v 1 with many fighters of the 4th gen era that may not be considered modern anymore. However in the right hands and with the right weapons and avionics fit no aircraft is ever at an incredible disadvantage.
The Phantom was an awesome platform in its day. It still looks mean to this day even on sticks.