Some phones like to do a jig on a hard surface until they fall off and give their owner a heart attack at the thought of a cracked screen. Others rotate quietly in small increments. Some feel hollow in the hand when they vibrate, while others give a vibration as solid as their construction. Due to a number of factors, each phone vibrates differently. The key factor at the core of it all, however, is how the motor works, and that technology has been changing and improving since the dawn of the cell phone. There are a few different types of vibration motors and patterns; some are made for a strong, attention-grabbing shake, while others, like the new Taptic engine in the iPhone 7, are made to be precise and even mimic things that you would normally touch or press.
At the most basic level of things, any phone's vibration works via a small motor moving a small part, or perhaps a few, rapidly. Differences in the shape of the motor's weights, the weight of the whole setup, and patterns or types of movement make for a different feeling for the consumer. Naturally, the structure of the phone plays a big part; the Nexus 6, for example, is a solid, heavy device. Its vibration motors have to be strong to pass vibration all through the mostly glass and metal body, one of the biggest of any phone out there, and as a result, you end up with a solid vibration that feels strong, but not overwhelming, being dampened by what's around it. The original Galaxy S, on the other hand, had a chin at the bottom that was partially hollow, and its body was mostly plastic. These factors, combined with a meager motor, made for haptic feedback that felt like knocking on an empty wooden box, and vibrations that were strong in your pocket, but not that loud or aggressive about bouncing off of tables.
Some phones boast a coin-shaped motor that rotates around a centrifuge. If you've ever owned a clear game controller, it's similar to what you see inside there, but thinner and much smaller. Others use two motorized weights, with one heavier than the other. Yet other systems use a piece of material strung up on a wire, which is shaken back and forth quickly, called a linear actuator. All of these mechanisms can produce a wide range of different vibration types, but have a few key characteristics that are common among all or nearly all phones sporting them. Counterweight systems have strong vibration and tend to be loud, for example, while linear actuator systems are quieter when in the hand, but louder on a flat surface than some other solutions, despite the fact that they don't actually move much.
Even phones with similar mechanisms, such as the linear actuator found in both the Pixel XL and the iPhone 7, can produce very different results depending on a number of factors, as you can see in the video below. The iPhone's Taptic engine will do an okay job of getting your attention as you're being jostled in a crowd or focused on work with your phone in your pocket, but it more than makes up for that with precision. Tightly integrated haptic feedback gives the user interface an exclamation point of sorts, but does so in a very controlled manner that's related to what's on the screen. Likewise, vibration is used to simulate pushing a button if a user exerts pressure on the new iPhone's solid home button. The Pixel, on the other hand, uses a smaller actuator, but throws it around much more violently. This results in a stronger vibration, but the movement takes longer to dampen and thus to stop, making for a less precise experience. It will get the job done for email alerts and haptic feedback, but don't expect too much fine control over the intensity, pattern, and the like.