convert 8v charger to 5v to charge my phone

 

7805.

 

You need to drop 3 volts with a voltage regulator, diodes, etc.

If it were me, I'd go to a second hand store and buy a 5V adapter for a couple dollars.

 

While a 7805 would do I would just buy a 5 volt charger which a version made for either 120 VAC or 12 VDC cost about $5.00 USD I wouldn't bother converting or building anything. Amazon has a wide variety including 120 VAC, 220 VAC and 12 VDC flavors all under $10.00 USD and many under $5.00 USD. Considering under five bucks and I see the things everywhere including used in thrift stores for a buck I would not bother making a 8 volt unit into a 5 volt unit. I guess if I did I would use a simple LM 7805 Regulator.

Ron