I don't have a smart phone. It is armored against drops, it makes phone calls, and does text messages. Even if it could access web pages (it might handle simple ones), they would be too tiny for my old eyes to see. I don't ever intend to use my phone to try and pay for stuff.
Does Amazon ship fast? With Prime, yes. Not Prime, you take your chances. Is it the cheapest? VERY OFTEN, NO!
For ham radio gear, I'm close to one of the biggest sellers, Ham Radio Outlet. Stuff I buy there gets here as fast or faster than Amazon Prime. And it is always cheaper.
Coin/paper money/collectible books are reasonable on Amazon, but anyone selling coins or paper money on their Amazon reseller account is almost always marked up higher than specialty dealers.
Amazon is a "one-stop" shop, and is convenient, but with its business practices, if the CEO wasn't rich, I can't see him having many friends.
-- Tom