richi23, first you need to know how the NCOS is set up in your PBX, and what NCOS is currently assigned to all your phones.
Think of FRL as money for rides at the fair -- say, a ride takes $3 -- 3 FRL. If you only have 2 FRL, you can't ride. It is standard to assign the same level FRL as the NCOS, when one is building that datablock -- NCOS 1 to FRL 1, and so on, 0 - 7. I've seen some PBXs that didn't do that, so that needs to be checked.
Then you assign an NCOS to each phone. Then, you build RLIs and assign an FRL to each route entry. When someone makes a call, they need to have an NCOS with at least that FRL to be able to call out.
Now, if your phones are currently assigned an NCOS/FRL of less than 7, you can do as other posters have suggested. But do not assume anything. When I build a PBX, I assign NCOS of 5 as the highest level of permission for phones, leaving 7 for telecom techs and the like for local termination, and perhaps a "superuser" class with 6 as you envision. Other switches I have seen give a 7 to everybody. In that case, you are facing a great deal of reprogramming.
As you are not conversant in BARS/NARS programming, I suggest you have your service provider do this, or someone who is skilled in this. Otherwise, you may open yourself up for some very unpleasant phone bills.