I've had several games as both Jason and the counselors where the phone is repaired within the first few minutes, as the counselors it quickly becomes a game of camp out and wait until they can make a mad dash to the main road and get away. For Jason suddenly your priority is on the main road to prevent an escape, especially if the players are spread out. I can't complain too much about either method because, although I never even saw a phone in any games I played, I definitely took the opportunity to escape as soon as it was repaired and the cops were on the scene.
The only suggestion I have regarding this would be to perhaps have the cops stay a maximum of five minutes before they leave, citing the thing as a prank call. Then give a two minute window or something before the phone can be used again, otherwise the cops will blow you off and think you're being an asshole. Or have the cops refuse to come back out at all! It happens in horror movies all the time!
If each game is twenty minutes long and the cops are called within the first few minutes then it becomes a game split into two halves once the cops have been called. If the cops leave then Jason still has another eight to ten minutes of gameplay without having to worry about returning to the main road for the entire fifteen minutes of the match while the laziest cops ever sit around outside the camp grounds.
Another thing that could be implemented is that if the cops arrive and no counselor is there within the first ninety seconds they could turn around and leave, citing it as a prank call courtesy of the Jason legend. Maybe the timer until the cops leave could be extended by twenty seconds or so for each survivor that manages to get out, giving people an incentive to work together.
A couple of things which might not be too balanced could be that, to prevent Jason camping at the main road, if Jason is there to greet the cops they stay at the lake for ten minutes instead of five, because that way they know for sure that there is shit going down. I figure this could give counselors camping out an advantage and too quickly make the game a hassle for Jason though. Another out-there thing could be that the higher the counselor's composure the longer the police could be convinced to stay for? Those who are scared out of their minds would be less able to form a coherent argument and more likely to want to get the fuck out, for example.
These could be completely awful suggestions of course but I think that having the cops stay for the duration of the game does make it a little easy for the counselors to get away.