Display embedded YouTube videos on iPhone

Open the Settings app, under General find Restrictions. Set the YouTube app to On.
Unless you did a “jailbreak” that interferes with YouTube, your embedded video should display.

Embedded YouTube videos not working on your iPhone? Try this fix

For embedding videos on YouTube, use HTML like this:

and CSS like this:

video, .video embed, .video object, .video iframe {
	width: 100%    !important;
	height: auto   !important;
}
.videoWrapper {
	position: relative;
	padding-bottom: 56.25%; /* 16:9 */
	padding-top: 25px;
	height: 0;
}
.videoWrapper iframe {
	position: absolute;
	top: 0;
	left: 0;
	width: 100%;
	height: 100%;
}