I am sorry, but you don't need to buy a new smartphone every year or every other year, or even three years.
You see, people stopped replacing PCs every year because both hardware and software have already reached a level of maturity, and further improvements to the OS are not much needed any more.
I think the smartphones are also been reaching this kind of a plateau for a while. For example, using the iPhone 4S I got only something like four years ago is a miserable experience today, it's just too slow, but the smartphone hardware has improved so much in the recent time that by now I think really _need_ to replace my smartphone ONLY when it breaks physically, which is not inconceivable for any mobile device. For example, the LG/Google Nexus 5 which was released in late 2013 and sold for the budget price of well under 400USD is still perfectly adequate smartphone today, and the SoC is actually still better than the one on many entry level or mid-range smartphones.
To contrast with the PC hardware, the Intel CPUs now improve only by 10-15% between the major generations, which is not a whole lot. On the other hand, the smartphone SoCs can continue improving at a much faster pace, but I think this process is now slowing down too, and will slow down even more.