I realize this question was posted in 2017 but considering it still shows up as a top result on Google I figured I’d provide an updated answer. You can now send an email as an attachment on the iPhone (at least I could on the iPhone X) although it was a little weird how I had to do it.
1) Click on the email you want to send as an attachment.
2) Click on the arrow at the bottom of the email and click the print option.
3) Hold your finger down on the picture of the email that shows up on the print screen until it pops up onto a new full sized screen.
4) Click on the “move to folder” button on the top right and from there you can select your email which will attach a copy of the email to a new email.