Turned phone off to charge and will not come back on

An iPhone 4? It's possible the device has quit altogether given it's age.

But just in case, follow the instructions in this support article > If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

I would recommend force restarting your phone, which you can do by following the steps outlined in this support article. I hope that helps!

Try force restarting the device by holding down the power button and home button for about 10-15 seconds. If you see an image on the screen after that, you're good to go. If you don't, wait about 45 seconds, then try flipping the vibrator switch back and forth. If you feel the phone vibrating, your screen may have died. If you don't have a password on the device, you should be able to pull the data off the phone with iTunes. Unfortunately due the the age of your phone, Apple considers it vintage and no longer works on it. If your phone isn't functional after the reset, it may be time to get a new one.