Is there a good email app with text-to-speech for iPhone?
Speak Screen
From email to books, let your iPhone read to you. If you
have a hard time reading the text on your iPhone, use Speak Screen to
read your email, iMessages, web pages, and books. Turn on Speak Screen
and swipe down from the top of the screen with two fingers, or just
tell Siri to Speak Screen and have all the content on the page read
back to you. You can adjust the voice’s dialect and speaking rate, and
have words, sentences, or words within sentences highlighted as
they’re being read. And the new Speech Controller provides a Speak
Under Finger feature for more precise control.

https://www.apple.com/accessibility/iphone/vision/
From the Home screen, go to Settings → General → Accessibility → Speech → Speak Screen. Or simply search using the search bar in Settings. To read screen, imagine bringing down notification centre, but with two fingers.
For single words: select them, and find &quot;Speak&quot; in the tooltip options that appear.
RSS reader for iPhone with text-to-speech support?