Google PRINCIPLES OF MOBILE SITE DESIGN: DELIGHT USERS AND DRIVE CONVERSIONS - Manual (Page 9)

3. MAKE IT EASY
TO GET BACK
TO THE HOMEPAGE
When mobile users navigate through your site,
they want an easy way to get back to your initial
homepage. In the study, participants usually
expected tapping the logo at the top of a page
to take them back to the homepage, and became
frustrated if it didn’t work.
Example from 1800 Flowers Mobile Site.
Key Takeaway
Use your logo as a navigation button
to return to the homepage.