Folks loved the startup chime that sounded off anytime a Mac was turned on. So much so that it went away, but Apple brought it back with the macOS 11.
There was never really was an official startup chime for the iPhone.
Well…there still isn’t, BUT if you have an iPhone 14, you can add a startup chime by utilizing an accessibility feature that helps those with visual impairments know when they have successfully powered off (and on) their device.
If you go to iPhone Settings > Accessibility > Audio/Visual you can toggle on “Power on and Off Sounds” icon.
Now when you turn off/on your iPhone 14, you will get a little chime. Not the same chime present in a Mac, but still…