The size and weight of a phone is usually determined by a phone's screen size. Choosing a phone means you'll be faced with many options touting displays of 4.3 inches or larger, some as big as 5.3-inches. Some of the smaller ones range between 3.2 to 3.7-inches, depending on various factors. However, do remember that depending on the size of your hand, it can actually be very difficult to use a device one-handed once you get into the bigger smartphones range.
Screen sizes are admittedly a subjective factor; as with tablets, there is no one size that fits all. However unlike tablets, the sizes for touchscreens for phones are more varied. Ultimately, it boils down to user preference, and personal comfort level with the display sizes.
Here's a quick actual size comparison of phone screen sizes (source: http://phone-size.com/) for a better gauge of what you as a user will be getting yourself into. The phones below represent just a fraction of what's available in the smartphone market and we must point out that there are other screen sizes available:
Display sizes also share a correlation to the tablet's battery life and weight. Typically speaking, a larger display will see higher power consumption and tend to be heavier to handle. Conversely, a smaller screen will see a better battery life (subjected to the battery capacity of the device) and is far easier to handle. Also, viewing on a smaller screen might be more straining on the eyes.
The display resolution is also intricately tied to your display choice. With a higher pixel count, you can expect sharper details and better video quality on your touch screen. A larger display size usually brings with it a higher pixel count to improve the clarity and sharpness of its displayed content.
As such, be aware of the display's resolution when you are looking at larger displays to avoid getting sub-standard images and video quality. Most phones released in 2011 generally come with bigger touch screens (4.3-inch and above) and a QHD (960 x 540 pixels) resolution. The Samsung Galaxy Nexus (4.65-inch) is the only one in the market with a (1280 x 720 pixels) HD resolution. Typically, phones with smaller screens (3.2-inch and below) typically come with a HVGA (320 x 480) resolution.
Likewise, a higher display resolution can lower the battery life of your smartphone. A larger screen usually sees a higher display resolution (thus, a higher pixels per inch density) to sharpen the details of the returned images and videos. However, if you are not too picky with the screen quality, the pixel resolution won't be a crucial factor.
Tip: A larger display should see a higher screen resolution to compensate for the pixels per inch density. However, be wary of the potentially lower battery life due to the combination of both features.
With screens getting bigger, screen technology is becoming increasingly important to consumers. Manufacturers like Samsung and Motorola choose to use terms like "Super AMOLED Plus" and "Super AMOLED Advanced PenTile" to sell this technology to the consumers. Most current phones are modeled around AMOLED (active-matrix organic light-emitting diode)-based displays; standard LCD display are usually seen in budget smartphones. With that said, both types have their disadvantages and advantages. AMOLED displays have the distinct advantage of a richer color reproduction, richer blacks, superior outdoor visibility in sunlight and better power management. Nonetheless, since the cost of the display is also proportional to the size, this is the likely reason for the slower adoption of this new display technology.