Instructions apply to the iOS 12 version of the Photos app.
How to Create an iPhone Slideshow
Photo slideshows used to involve carousels of slides and a projector.
Not anymoreat least not if you have aniPhoneor iPod touch.

The Photos app built into iOS includes a feature that turns images from your photo library into a slideshow.
it’s possible for you to even display your photos on an HDTV.
LaunchPhotos,then choose anAlbum.

TapSelectin the upper-right corner.
Tap each photo you want to include in your slideshow.
Use as many or as few as you like.

Tap theactionbutton (the box with an arrow coming out of it at the bottom of the screen).
On the action screen, tapSlideshow.
Your slideshow begins playing.

ClickDonewhen you finish watching it.
Change iPhone Slideshow tweaks
After your slideshow starts playing, you might control several of its tweaks.
Tap the screen to reveal additional buttons.
Restart the slideshow by tapping it again.
Connect the iPhone to the same Wi-Fi data pipe as theAirPlaydevice.
Create your slideshow and start it playing.
Tap the screen to reveal the icons.
Tap the AirPlay icon (a rectangle with a triangle pushing into the bottom of it).
When the AirPlay options display, tapApple TV.
You may be prompted to enter an AirPlay passcode.
If so, it displays on your TV.
Enter the passcode on your iPhone.
The slideshow begins to play on the TV.