Problem with shopping cart on phones

Many customers always have trouble adding to cart, where the vast majority use phones to make purchases. Apparently phone browsers have a navigation bar that does not allow to see the add to cart button. I attach a video link, this is a very problematic problem, the only solution is to give the link directly to the customer which is quite redundant, this site is embedded to Google Sites a tool used to gather all the content of my business and give the link directly from the catalog would discard the function that has Google Sites in my business.

Link video: Watch Problem embed, shopping cart. | Streamable

A possible solution is that from the administrator or configuration of the site, this the option to make the cart bar is fixed or placed before the product description and so the customer on the phone will not have problems with the navigation bar of your browser.
Clearly this is a solution for developers to consider. I hope you see my idea about the problem thank you.