In the iPhone world we don't have the freedom to change much, especially the app launcher (Springboard) which is installed and maintained by Apple.
If you happen to have iOS 9.1 or lower, you can go through a process called Jailbreak where you can install software that is not from the iTunes Store and get some neat features. I had an iPad on iOS7 that was jailbroken for several years until I upgraded it to get some new features.
There are alternate Springboards and App management tools, as well as Apps when you are outside of the Apple jail. You can also brick your system, and get a virus, so be careful, follow steps carefully. I get my info on this at reddit
https://www.reddit.com/r/jailbreak where in the side bar you can see what versions of iOS have been broken and the team with the steps to free your iPhone from Apple jail.
When my iPad had a jailbreak on it, I had ad blocking in the Safari browser, and an alternate Spring Board that would allow me to have as many buttons as I wanted on it, with options to scroll the bar as well. But I also lost the use of some applications that could detect the jailbreak and refuse to run.
If you are on iOS 9.2 or higher, you are stuck with what you have. You can do things like move useless application (iTunes Store, News, Stocks, Tips, Watch) into a folder, then put the folder on a page at the end by itself.
You can look for alternate apps, like Overcast instead of Podcasts, Google Maps instead of Apple Maps (too bad you can't make Google Maps the default mapping software), Chrome instead of Safari (too bad you can't run plugins or make Chrome the default browser), or the Ad Block Plus Browser (not as stable as Safari, but at least it is free ad blocking).
On the iPhone you can install alternate keyboards. You'll have to be on iOS 9.0 or higher, but at least that is there. If you are on an iPhone 5s or better, you can install an ad blocker to Safari as a plugin, also requires iOS 9.0 or better.
You can't choose the iOS you are running. You are either on the one you have or upgrade to the latest. There is no in between.
On the positive side, there are significantly less security flaws on iOS (assuming no jailbreak) since StageFright is not on it exposing the entire phone to remote take over attacks. You have almost no virus risk on iOS (99.7% are on android), the apps on iOS are generally playing nicely and not stealing your personal data. And you know that Apple is not willing to break into your phone for the government, and are trying to make it so they can't ever do it.