Here are some instructions for a number of ways to get a Leanpub book onto your phone:
Pro tip: If you are trying to download a book onto your iPhone, it won't work if the link is being opened in Chrome. It will work if you try to open the link in Safari. If none of the options in the article linked to above work, you can try following these steps:
- Copy the EPUB link from the email
- Open Safari (or a browser that is not Chrome) on your phone
- Paste the EPUB link in the address bar and click "Go"
- Click on "Open in iBooks"
If you are using an Android phone, a similar process (with different apps) might work.