how do i get the battery percentage to show on my phone

On your iPhone 13 swipe down from the top-right corner. The battery percentage is viewable while in any app, as well as from the Home Screen and Lock Screen.

From the iPhone User Guide (iOS 15):

See the iPhone battery percentage in the status bar

• On an iPhone with Face ID: Swipe down from the top-right corner.
• On an iPhone with a Home button: Go to Settings > Battery, then turn on Battery Percentage.

Unfortunately it won’t display a numeric %’age on the battery icon of main/home screen (like on a Mac).

The closest you can get is to activate the Battery Widget.

Then, battery state displays on a nice big screen w/ a single right-swipe from the home screen.

See:

Use widgets on your iPhone and iPod touch - Apple Support

I see this question all the time, yet there’s one answer that I’ve never seen in these forums. And it’s always worked well enough for me, on the rare occasions when I’d like a number rather than the perfectly adequate graphic battery icon.

”Hey Siri, how’s your battery?”

You’re welcome.