I need some wires inside my phone cleaned. And the only alcohol I can find is 70%. Is it safe to clean electrical wires with it? Or would that be too much water?
It might be okay, however usually we use 99% IPA, which has to be ordered from chemical suppliers (and is considered hazardous since it's quite flammable). It's usually okay to clean with water, so provided the water was pure and was allowed to dry before power was applied it might be okay to use water+IPA and a soft brush.
Another concern is what exactly is in the remaining 30%. If it is drug-store (pharmacy) "rubbing alcohol" it may contain other additives that can leave a residue which could affect the operation of electronics. Most of the stuff available from local pharmacies here leaves a nasty white residue, and I would not suggest using it.
There is no need to be concerned whether or not 70% IPA is good for electronics due to its water content, because there is no need to ever buy or use anything other than "99%" IPA.
70% IPA isn't good for anything. If you should ever discover the preceding statement to be false, you can make 70% aqueous IPA easily from pure IPA.
I often use n-propyl bromide (marketed as Ensolv) for both flux removal and as a general cleaning solvent. It's flux removal ability is nothing short of magical, but it will dissolve some plastics, so be careful. The good thing about it is that it leaves zero residue of any kind, which 70% isopropyl might. I find it also works on cleaning wires and PCBs better than isopropyl.