Welcome to Android Central! Was the phone factory reset before you got it? If not, did you reset it, or are you still using the previous owner's account?
Make sure the phone is logged in with your Google account, not someone else's. I'm not sure why the browser is asking for your mobile number, though. Is there a website asking for it, or is it in a popup?
The factory reset was done before I got it. I loaded all my accounts but when I try to pull up both Chrome & stock internet browser I get to screen that asks for mobile #. When I enter it I get this in the address bar: http :// vision.sprintpcs.com/?errorMessage=true (minus the spaces)
Does the Chrome browser on your S5 have the option to set a homepage? I know that Chrome on some Samsung devices does have this option (while Chrome for most other devices doesn't). Open Chrome, tap Menu>Settings, and look for an option to set a homepage. See if it's set to some kind of Sprint site, and change it if possible. Do the same on the stock Internet browser.