This also came up a few months ago, after some tweaks because of problems with the MiG-31/AA-9 combo back in October.
I tried out a number of different planes, and my conclusion wasn't that the F-14/Phoenix combo was exceptionally good, but rather that the MiG-31/AA-9 combo had become anomalously bad. While it used to be effective out near max range, much like the Phoenix, now it can only achieve around 52 nm.
Here's comparative results of testing different SARH systems (F-4, F-15, MiG-25, F-14, MiG-31) vs fighter and bomber targets.
You can see how the MiG-31 system is proportionately much worse than other systems. It's only detecting the fighter targets at ~ 42% of its maximum radar range, compared with 70% or 82% or 84% or 91% for an F-4 or F-14 or F-15 or MiG-25, and its only illuminating at ~ 31% of its maximum range. If it acted in similar proportion to the other systems, you would expect detections out around the 120 to 150 nm range. The slightly older F-14 is getting 147 nm detections, so why not the Mig-31? It's only getting half the F-14's detection range (and that's purely a radar issue, before the missile enters the equation).
Spot the outlier!
Look-down clutter is not a differentiating issue here, since the planes in the test scenario are all at the same altitude. I also tried with the MiG-31 one altitude band lower than the target, and got the same range results.
The fact that the MiG-31 system had a lower range than the F-15/Sparrow system seems counter-intuitive. The raw power of the Flash Dance is significantly higher (1.7 times more range) than the AN/APG-70, and the antenna on the missile is also significantly larger. The AA-9 has a 15" diameter body, while the Sparrow is only 8". For a crude order of magnitude comparison, knocking off 1" for radome thickness and antenna clearance, the AA-9 has roughly four times more signal gathering antenna area than the Sparrow. Wouldn't that mean it could detect the same echo at roughly twice the range?
So I think the question is not "why is the F-14 so good?", but rather "why did the MiG-31 become unusually bad?"