There is but you can't do anything useful with it like login or submit reviews.
Yelp has a policy that bars reviews written on mobile devices. This is done to protect the quality of the reviews.
You can't submit reviews from an iPhone either. The functionality doesn't exist.
In Android, you can submit reviews written via a browser, just not via the Yelp app. Via the app, you can write and submit "quick tips" (which are often short reviews) and draft regular reviews with a star rating on your mobile device, but then you have to open the browser to submit them.
Are you just making this up? I just did that with my iPhone Yelp app right now.