How do I break a concrete slab without damaging cabling running through it?
If you need to maintain the existing phone cable, leave it alone. Actually, even if you're not planning on using the existing phone cable, just leave it alone.
If you want/need to run the fiber close to the existing cable, drill a new hole. That will give you a neat, tidy opening you can run the fiber through and shouldn't cause any damage to the existing cable, so long as you're not trying to get too close to it.
Optionally, run the fiber in a totally different location. Bring it to the slab, then run it up, in EMT or Schedule 80 PVC (for protection on the outside of the house), until you hit wood, then go in through the wood instead of through concrete. This will make all your work much easier as any work to get through wood is much easier than any method of getting through concrete.