By default, the live photos and videos auto play on the Photos app in iPhone.
If you are not a fan, then you can disable it.
Disable Auto Play of Videos and Live Photos
Step 1: Open Settings.
Step 2: Hit Photos.
Step 3: In Photos Tab section, you can see Auto-Play Videos and Live Photos.
Step 4: Beside it, you can a toggle switch. Disable it.
That is all. From now on, the videos and live photos does not auto play on Photos app.
Note: To revert, follow the above steps but instead of disabling toggle switch, enable it.