Phone friendly web design does require some unique considerations that change how your visitor will interact with your site. Here are some of the top suggestions.
1. Be Fat Thumb Friendly
Phones are getting bigger and bigger and in some ways that helps as far as images and visual appeal. But if you need to navigate the site and your home page is a touch on the top left, that's a stretch for a right handed person on a big phone. My phone allows you to resize the display for comfortable thumb navigation, but not all phones do this.
Beyond that, phone numbers should be touch friendly. Any phone number can be hyperlinked so that when you click it, it opens that number as a new call. If the phone number on the page is too small, it's hard to select it. Make phone numbers and anything click-able big, bold and obvious.
2. Minimize page detail
I think in a year or two there will be a medical condition associated with scrolling a website with your thumb. It's not a natural motion. We are a society with more and more wants and shorter and shorter memory. There are two modes of thought trending relative to phone design and they are quite opposite. One is, keep it all on one page. You navigate literally by moving the page up and down. The other is keep the pages short and to the point. Give clickable options and anticipate the likely travel path of the user. From a strictly SEO standpoint I like the latter but both can be effective.
3. Minimize picture detail
Pictures will resize to accommodate the size of the phone. Detail will disappear. If your pictures don't look good as thumbnails (200 pixels wide is a good standard), they probably won't work for your phone
4. Make galleries touch friendly
It's better if you can have galleries be swipe friendly. If you want to move from picture to picture, often the tiny arrow that moves you from picture to picture is hard to find and even harder to touch and make work. Intuitively, you want to be able to swipe left or right and the pictures in the gallery to move accordingly.
5. Make site device and rotation friendly
Every time we build a site we have to check it in a variety of browsers. Now, in addition to that, we have Android smart phones, iPhones, and tablets. A site has to work in a variety of situations including the vertical and landscape rotations of those devices.